Total synthesis of (+)-nankakurines A and B and (±)-5-epi- nankakurine A

pubs.acs.org/joc

Total Synthesis of (þ)-Nankakurines A and B

and (()-5-epi-Nankakurine A

Ryan A. Altman,^†Bradley L. Nilsson,^†,§Larry E. Overman,*^,†Javier Read de Alaniz,^{†,^}

Jason M. Rohde,^†,and Veronique Taupin^‡

^†Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697-2025,

United States, and ^‡Aging Department, Sanofi-Aventis R&D, 1 Avenue Pierre Brossolette,

91385 Chilly-Mazarin, France. ^§Current address: Chemistry Department, University of Rochester,

Rochester, NY 14627. ^{^}Current address: Department of Chemistry and Biochemistry,

University of California, Santa Barbara, CA 93106-9510. Current address: Ironwood Pharmaceuticals,

Inc., 301 Binney Street, Cambridge, MA 02142.

leoverma@uci.edu

Received August 17, 2010

The first total syntheses of the Lycopodium alkaloids (þ)-nankakurine A (2), (þ)-nankakurine B (3),

and the originally purported structure 1 of nankakurine A were accomplished. The syntheses of 2 and

3 feature a demanding intramolecular azomethine imine cycloaddition as the key step for generating

the octahydro-3,5-ethanoquinoline moiety and installing the correct relative configuration at the

spiropiperidine ring juncture. The cyclization precursor was prepared from octahydronaphthalene

ketone 50, which was assembled from enone (þ)-9 and diene 48 by a cationic Diels-Alder reaction.

The Diels-Alder reactants were synthesized from 5-hexyn-1-ol (16) and (þ)-pulegone (49), respec-

tively. The tetracyclic ring system of 1 was generated using an unprecedented nitrogen-terminated

aza-Prins cyclization cascade. The enantioselective total syntheses of (þ)-nankakurine A (2) and (þ)-

nankakurine B (3) establish the relative and absolute configuration of these alkaloids and are

sufficiently concise that substantial quantities of 2 and 3 were prepared for biological studies. (þ)-

Nankakurine A and (þ)-nankakurine B showed no effect on neurite outgrowth in rat hippocampal

H-19 cells over a concentration range of 0.3-10 μM.

Introduction

spiro stereocenter of nankakurine A was assigned on the

1

basis of H NMR NOE experiments and concurred with

Because of their diverse architectures and biological activ-

ities, Lycopodium alkaloids¹have attracted significant syn-

thetic interest for many years. In 2004, Kobayashi and

co-workers reported the isolation of a structurally unique

Lycopodium alkaloid, (þ)-nankakurine A,²from the club

moss Lycopodium hamiltonii collected at the southwest tip of

Kyushu Island, Japan. On the basis of two-dimensional

NMR data and mass spectrometric analysis, structure 1

was proposed (Figure 1).²The relative configuration at the

(1) For reviews of the Lycopodium alkaloids, see: (a) Kobayashi, J.;

Morita, H. In The Alkaloids; Cordell, G. A., Ed.; Academic Press: New York;

2005; Vol. 61, p 1. (b) Ma, X.; Gang, D. R. Nat. Prod. Rep. 2004, 21, 752–772.

(c) Ayer, W. A.; Trifonov, L. S. In The Alkaloids; Cordell, G. A., Brossi, A.,

Eds.; Academic Press: New York, 1994; Vol. 45, p 233. (d) Ayer, W. A. Nat.

Prod. Rep. 1991, 8, 455–463. (e) MacLean, D. B. In The Alkaloids; Brossi, A.,

Ed.; Academic Press: New York, 1985; Vol. 26, p 241. (f) MacLean, D. B. In

The Alkaloids; Manske, R. H. F., Ed.; Academic Press: New York, 1973; Vol.

14, p 348. (g) MacLean, D. B. In The Alkaloids; Manske, R. H. F., Ed.;

Academic Press: New York, 1968; Vol. 10, p 305.

DOI: 10.1021/jo101619d

r

Published on Web 10/19/2010

J. Org. Chem. 2010, 75, 7519–7534 7519

2010 American Chemical Society

Altman et al.

JOCFeatured Article

SCHEME 1. Retrosynthetic Analysis of 5-epi-Nankakurine (1)

FIGURE 1. Nankakurines A and B and two structurally related

Lycopodium alkaloids.

polar functional groups known to negatively affect central

nervous system exposure of small-molecule drugs.⁹

Stimulated initially by the opportunity to explore a new

construction of polycyclic diamines (vide infra) and by the

prospect of obtaining sufficient quantities of nankakurines A

(2) and B (3) to evaluate their potential as leads for develop-

ing new agents for combating neurodegenerative disorders,

we initiated a total synthesis program in this area.¹⁰Herein,

we report the development of the chemistry that allowed the

first total syntheses of (þ)-nankakurine A, (þ)-nankakurine

B, and the originally proposed structure of nankakurine A

(1) to be accomplished, syntheses that confirmed the relative

configuration and established the absolute configuration

of these rare alkaloids.¹¹Moreover, these syntheses allowed

the neurotrophic activities of both 2 and 3 to be examined. In

this exploration, neurotrophic activity was not observed in

rat hippocampal H-19 cells over a concentration range of

0.3-10 μM.

the structure of spirolucidine (4), whose relative configura-

tion had been secured earlier by single-crystal X-ray anal-

ysis of a derivative.³

Two years later, the Kobayashi laboratory reported that

further purification of this club moss extract provided a less

abundant alkaloid, (þ)-nankakurine B, for which structure 3

was suggested.⁴In this case, ¹H NMR NOE data were

interpreted to support a configuration at the spiro stereo-

center opposite to that originally proposed for nankakurine

A (1). Reductive methylation of natural nankakurine A gave

nankakurine B, thus, the structure of nankakurine A was

revised to 2.⁴

Neurotrophic factors play an important role in mediating

neuronal growth and can counteract neuronal atrophy and

death in the adult nervous system.⁵Because of the poor

pharmacokinetics documented by naturally occurring poly-

peptidyl neurotrophic factors,⁶small molecules that exhibit

neurotrophic effects are attracting considerable attention

as potential therapeutics.⁷Thus, Kobayashi’s disclosure in

2006 that nankakurine A (2) induced secretion of neuro-

trophic factors in human astrocytoma cells at a concentra-

tion of 1 μM heightened our interest in this area.⁴Similar

examination of nankakurine B was not possible at the time as

a result of the low abundance of these alkaloids in their

natural source.⁸It was particularly provocative that nankak-

urines A and B bore no obvious structural relationship to

other small-molecule neurotrophic agents reported at that

time⁷and, moreover, that their structures were devoid of

Results and Discussion

Initial Retrosynthetic Analysis. The focus of our initial

effort was the originally purported structure 1 (5-epi-nankak-

urine A) of nankakurine A (Scheme 1). We envisioned

tetracyclic diamine 6 arising in one step from bis-homoallylic

amine 8 by an amino-terminated aza-Prins cyclization of

formaldiminium intermediate 7 (Scheme 1). Although car-

boxylate-terminated aza-Prins reactions of amino acids had

been described,¹²amino-terminated aza-Prins cyclizations

were unknown. This lack of precedent provided extra moti-

vation for evaluating this approach, as we envisioned amino-

terminated aza-Prins cyclizations potentially having consid-

erable utility in heterocyclic synthesis. Cyclization of the

tethered nitrogen nucleophile from the sterically less hin-

dered convex face of intermediate 7 was expected to set the

(2) Hirasawa, Y.; Morita, H.; Kobayashi, J. Org. Lett. 2004, 6, 3389–

3391.

(3) Ayer, W. A.; Ball, L. F.; Browne, L. M.; Tori, M.; Delbaere, L. T. J.;

Silverberg, A. Can. J. Chem. 1984, 62, 298–302.

(4) Hirasawa, Y.; Kobayashi, J.; Obara, Y.; Nakahata, N.; Kawahara,

N.; Goda, Y.; Morita, H. Heterocycles 2006, 68, 2357–2364.

(5) (a) Dawbarn, D.; Allen, S. J. Neuropath. Appl. Neurobiol. 2003, 29,

211–230. (b) Dauer, W. Science 2007, 411, 60–62.

(9) Hitchcock, S. A.; Pennington, L. D. J. Med. Chem. 2006, 49, 7559–

7583.

€

(6) Kirik, D.; Georgievska, B.; Bjorklund, A. Nat. Neurosci. 2004, 7,

105–110.

(7) (a) Hefti, F. Annu. Rev. Pharmacol. Toxicol. 1997, 37, 239–267.

(10) Portions of this work were described in an earlier communication:

Nilsson, B. L.; Overman, L. E.; Read de Alaniz, J.; Rohde, J. M. J. Am.

Chem. Soc. 2008, 130, 11297–11299.

ꢀ

(b) Luu, B.; Gonzalez de Aguilar, J.-L.; Girlanda-Junges, C. Molecules

(11) After our studies in this area were concluded, an efficient construc-

tion of (()-2 and (()-3 from (()-luciduline (5) was described: Cheng, X.;

Waters, S. P. Org. Lett. 2010, 12, 205–207.

(12) (a) Heathcock, C. H.; Ruggeri, R. B.; McClure, K. F. J. Org. Chem.

€

1992, 57, 2585–2594. (b) Logers, M.; Overman, L. E.; Welmaker, G. S. J. Am.

Chem. Soc. 1995, 117, 9139–9150.

2000, 5, 1439–1460. (c) Waters, S. P.; Tian, Y.; Li, Y.-M.; Danishefsky,

S. J. J. Am. Chem. Soc. 2005, 127, 13514–13515. and references therein.

(8) The scarcity of the natural nankakurines (2 and 3 were isolated in

0.0003 and 0.0002% yields, respectively) prevented evaluation of the neuro-

trophic properties of the less abundant nankakurine B (3).⁴

7520 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

spiropiperidine stereocenter of 1 with high selectivity. We

foresaw the central challenge in orchestrating a successful

amino-terminated aza-Prins reaction as co-generating and

properly matching the iminium ion electrophile and the

nitrogen nucleophile. cis-Octahydronaphthalene amine 8

was seen deriving from the Diels-Alder reaction of (R)-5-

methyl-2-cyclohexen-1-one (9) and diene 10, a strategy

that drew ample precedent from Oppolzer’s pioneering

early synthesis of (þ)-luciduline.¹³

SCHEME 2. Synthesis of cis-Octahydronaphthalene Amine 22

Synthesis of cis-Octahydronaphthalene Amine Intermedi-

ates. Our early exploratory studies were carried out in the

racemic series and required convenient access to 5-methyl-2-

cyclohexen-1-one ((()-9) and 1,3-diene 19 (Scheme 2). After

examining several of the known methods for preparing

cyclohexenone (()-9,¹⁴we developed an alternate synthesis

from 5-methyl-1,3-cyclohexanedione (13), which is commer-

cially available or readily prepared from inexpensive orcinol

(11) by methylation¹⁵followed by Birch reduction and acidic

hydrolysis.¹⁶Reaction of dione 13 with oxalyl bromide to

form β-bromoenone 14¹⁷followed by reduction with zinc

in THF gave 5-methyl-2-cyclohexen-1-one ((()-9) in 55%

overall yield from orcinol. As noted by Cossy,¹⁸attempts

to prepare ethylene ketal 15 from (()-9 by reaction with

ethylene glycol in the presence of a variety of Brønsted acids

under Dean-Stark conditions were complicated by migra-

tion of the double bond to provide significant amounts of

9-methyl-1,4-dioxaspiro[4.5]dec-7-ene. Although the use of

the weak acid pyridinium p-toluenesulfonate (PPTS) allowed

ketal 15 to be prepared in 29% yield (55% based on con-

sumed (()-9),¹⁸this ketalization was more efficient (73%

yield) when carried out by reaction of (()-9 with 1,2-bis-

(trimethylsiloxy)ethane and catalytic trimethylsilyl triflate

(TMSOTf) at -78 ꢀC.¹⁹

Using a Mitsunobu variant of the Gabriel amine synthesis,

diene 19 was prepared in a three-step sequence from 5-hexyn-1-

ol (16). Alcohol 16 was transformed first into amine hydro-

chloride salt 17, which was protected as a sulfonamide (18) in

83% yield for the two-step sequence.^20,21Reaction of alkyne

18 with ethylene using Grubbs’ second generation catalyst²²

afforded diene 19 in 90% yield.²³The TMSOTf-catalyzed

ionic Diels-Alder reaction²⁴of cyclohexenone (()-9 with

diene 19 took place in 50-60% yield using a stoichiometric

quantity of 1,2-bis(trimethylsiloxy)ethane. During attempts

to optimize this conversion, it became apparent that the

moderate yield arose from reaction inhibition resulting from

the buildup of (TMS)₂O. When ketal 15 was employed, the

ionic Diels-Alder reaction proceeded in high yield with

excellent cis-diastereoselectivity.²⁵Subsequent cleavage of

the ketal using FeCl₃adsorbed on silica gel^26,27provided

ketone 20 in 90% yield from diene 19.²⁸Ketone 20 was

quantitatively converted to cis-oxime 21 upon reaction at

room temperature with aqueous hydroxylamine in metha-

nol; the use of acidic or basic conditions for oxime formation

resulted in significant epimerization. The robust sequence

summarized in Scheme 2 reproducibly provided oxime 21 on

(13) (a) Oppolzer, W.; Petrzilka, M. J. Am. Chem. Soc. 1976, 98, 6722–

6724. (b) Oppolzer, W.; Petrzilka, M. Helv. Chim. Acta 1978, 61, 2755–2762.

(14) (a) Chong, B.-D.; Ji, Y.-I.; Oh, S.-S.; Yang, J.-D.; Baik, W.; Koo,

S. J. Org. Chem. 1997, 62, 9323–9325. (b) Nicolaou, K. C.; Montagnon, T.;

Baran, P. S. Angew. Chem., Int. Ed. 2002, 41, 1386–1389.

(15) Mondal, M.; Puranik, V. G.; Argade, N. P. J. Org. Chem. 2007, 72,

2068–2076.

(16) (a) Sardina, F. J.; Johnston, A. D.; Mourino, A.; Okamura, W. H.

~

J. Org. Chem. 1982, 47, 1576–1578. (b) Masaguer, C. F.; Ravina, E.;

Fontenla, J. A.; Brea, J.; Tristan, H.; Loza, M. I. Eur. J. Med. Chem. 2000,

ꢀ

35, 83–95.

(17) (a) Mewshaw, R. E. Tetrahedron Lett. 1989, 30, 3753–3756.

(b) Clark, R. D.; Heathcock, C. H. J. Org. Chem. 1976, 41, 636–643.

(18) Cossy, J.; Bellosta, V.; Ranaivosata, J.-L.; Gille, B. Tetrahedron

2001, 57, 5173–5182.

(19) Tsunoda, T.; Suzuki, M.; Noyori, R. Tetrahedron Lett. 1980, 21,

1357–1358.

(20) Illesinghe, J.; Campi, E. M.; Jackson, W. R.; Robinson., A. J. Aust. J.

Chem. 2004, 57, 531–536.

(25) Anderson, J. C.; Blake, A. J.; Graham, J. P.; Wilson, C. Org. Biomol.

Chem. 2003, 1, 2877–2885.

(21) In our early studies, sulfonamide 18 was prepared from 16 by

reaction with (cyanomethylene)tributylphosphorane and p-toluenesulfon-

amide; however, this reaction provided low yields (18-80%) in some runs.¹⁰

(22) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1,

953–956.

(23) For selected examples of enyne metathesis, see: (a) Hansen, E. C.;

Lee, D. J. Am. Chem. Soc. 2004, 126, 15074–15080. (b) Smulik, J. A.; Diver,

S. T. Org. Lett. 2000, 2, 2271–2274.

(26) Kim, K. S.; Song, Y. H.; Lee, B. H.; Han, C. S. J. Org. Chem. 1986,

51, 404–407.

(27) These mild conditions were important for conserving the configura-

tional integrity of the cis-octahydronaphthalene ketone product.

(28) We previously reported the use of an EtAlCl₂-catalyzed Diels-Alder

reaction to prepare decalone 20 in modest yield as a mixture of epimers (74%,

cis/trans = 1:1-1:3).¹⁰This mixture of compounds was converted under

kinetic control to a mixture of cis- and trans-oximes 21 under basic conditions

(>90% yield, 3:1-5:1 cis/trans). Pure cis-21 could be selectively precipitated

in 40-60% yield. For details, see refs 10 and 13.

(24) Gassman, P. G.; Singleton, D. A.; Wilwerding, J. J.; Chavan, S. P.

J. Am. Chem. Soc. 1987, 109, 2182–2184.

J. Org. Chem. Vol. 75, No. 22, 2010 7521

Altman et al.

SCHEME 4. Attempted Hydroamination of Tricyclic

Unsaturated Sulfonamides 24, 25, and 28

JOCFeatured Article

SCHEME 3. Attempted Nitrogen-Terminated Aza-Prins

Reaction of Cyanomethyl Amine 23

scales of >10 g. Reduction of this intermediate with MoO₃

and NaBH₄provided cis-octahydronaphthalene amine 22 in

excellent yield.²⁹

Exploration of Amino-Terminated Aza-Prins Cyclizations

and the Synthesis of (()-5-epi-Nankakurine (1). In our initial

attempts to develop an amino-terminated aza-Prins cycliza-

tion, we employed a cyanomethyl amine as a formal-

diminium ion precursor to allow the iminium cation to

be generated under mild conditions in various solvents.³⁰

Cyanomethylamine derivative 23 was prepared in 78% yield

by alkylation of amine 22 with chloroacetonitrile. Reaction

of this formaldiminium precursor with AgO₂CCF₃in CHCl₃

at room temperature gave the monocyclized product, octa-

hydro-3,5-ethanoquinoline 24, in nearly quantitative yield

(Scheme 3). Variation of the solvent or changing the initiat-

ing reagent to Cu(O₂CCF₃) led in no case to the formation of

detectable tetracyclic product. We also investigated related

reactions of congeners of cyanomethylamine 23 in which the

tethered nitrogen substituent was NH₂, NHBn, or NHC₆-

H₄p-OMe instead of NHTs; however, Ag-mediated cycliza-

tion reactions of these substrates also produced simple aza-

Prins products analogous to 24. In an attempt to see if a

potential tricyclic tertiary carbenium precursor of azatricyc-

lic 24 could be trapped by an external nitrogen nucleophile,

the silver-promoted cyclization of 23 was carried out in the

presence of 10 equiv of sodium azide. This reaction also led to

the formation of octahydro-3,5-ethanoquinoline 24 in high

yield.

Although it would be less desirable than a cascade se-

quence, we investigated briefly whether the spiropiperidine

ring could be formed in a subsequent step from aza-Prins

product 24 (Scheme 4). As intramolecular hydroamination

of unsaturated N-tosylamines to form pyrrolidine rings in

the presence of strong acids is well-established,³¹tricyclic

sulfonamide 24 was allowed to react with trifluoromethane-

sulfonic acid (TfOH) or trifluoroacetic acid (TFA, neat or in

toluene, rt to 80 ꢀC). These reactions generated double bond

isomers of 24 but no trace of tetracyclic product 26. In order

to minimize protonation at N1, aza-Prins product 24 was

protected as a methyl carbamate. Reaction of carbamate 25

with TfOH or TFA (neat or in CHCl₃, MeCN, or PhMe, rt to

100 ꢀC) resulted in the formation of multiple products,

including those that resulted from loss of the carbamate

and isomerization of the double bond; the desired tetracyclic

product 27 was not produced. In order to further reduce the

basicity of the protected amine and increase the stability of

this substituent, p-nitrophenylsulfonyl (Ns) sulfonamide 28

was prepared. Reaction of 28 with TFA or p-toluenesulfonic

acid (TsOH, 25-80 ꢀC, various solvents) returned only start-

ing material, whereas exposure of 28 to TfOH at 120 ꢀC

delivered tetralin derivative 29. This extensive degradation

presumably results from protonation of N1, followed by the

cleavage of two C-N bonds to eliminate p-nitrophenylsul-

fonamide, and finally double bond isomerization to produce

tetralin 29 (30 f 31 f 32).

A metal-catalyzed hydroamination reaction was consid-

ered as an alternative approach for preparing tetracyclic

products 26 or 27 from tricyclic intermediates 24 or 25;^32,33

however, existing literature precedent focuses largely on

substrates that contain only one nitrogen substituent and

(32) For recent reviews of metal-catalyzed hydroamination reactions, see:

€

(a) Muller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675–704. (b) Hultzsch, K. C.

Adv. Synth. Catal. 2005, 347, 367–391.

(33) Most late transition metals effect hydroamination by initial activa-

tion of the olefin, followed by attack of the amine nucleophile onto the alkene

from the face trans to the coordinated metal.³²For the metal-catalyzed

hydroamination of 24 or 25, the most sterically accessible face of the olefin

for metal coordination resides on the convex face of the tricycle, which would

require cyclization of the amine to occur from the concave face, and would

deliver the incorrect stereochemistry of the piperidine spirocycle. The steric

effect of the tricycle could inhibit this cyclization. Metals that promote

hydroamination by amine activation represent the most attractive catalysts

to prepare epi-nankakurine A (1).

(29) Ipaktchi, J. Chem. Ber. 1984, 117, 856–858.

(30) Overman, L. E.; Jacobsen, E. J.; Doedens, R. J. J. Org. Chem. 1983,

48, 3393–3400.

(31) (a) Schlummer, B.; Hartwig, J. F. Org. Lett. 2002, 4, 1471–1474.

(b) Haskins, C. M.; Knight, D. W. Chem. Commun. 2002, 2724–2725.

7522 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

SCHEME 5. Potential Nitrogen Participation in the Aza-Prins

Cyclization To Form Octahydro-3,5-ethanoquinoline 24

SCHEME 6. Attempted Sulfonamide-Terminated Aza-Prins

Reaction of Carbamates 37 and 39

typically result in the formation of pyrrolidine rings. There

are only a few examples that result in the formation of piperi-

dine rings or that utilize trisubstituted alkenes.³⁴Intramolec-

ular hydroamination of 24 and 25 utilizing FeCl₃was

evaluated.³⁵Extended exposure of unsaturated sulfon-

amides 24 or 25 to FeCl₃at 80 ꢀC in 1,2-dichloroethane

resulted only in slow conversion of the starting material to

mixtures of alkene-migrated products.

Being sensitized at this point to the ready formation of

alkene regioisomers in reactions of azatricyclic alkenes 24

and 25 with acids, we reconsidered the observation that pro-

duct 24 was produced as a single double bond isomer in the

original aza-Prins cyclization. This high regioselectivity sug-

gested the possibility that the nitrogen atom of the hydro-3,5-

ethanoquinoline fragment of 23 was participating in the

generation of the tricyclic aza-Prins product (Scheme 5). For

stereoelectronic reasons,³⁶aza-Prins cyclization of formal-

diminium ion 33 should generate initially tricyclic carbe-

nium ion 34, which would be expected to undergo rapid

nitrogen inversion³⁷to isomer 35, in which the nitrogen non-

bonded electron pair would be positioned ideally to assist in

deprotonation to form the conjugate acid 36 of octahydro-

3,5-ethanoquinoline product 24.³⁸

SCHEME 7. Sulfonamide-Terminated Aza-Prins Cyclization

To Form Spirotetracyclic Product 27

To enhance the lifetime of carbenium ion intermediate 35

and potentially favor a nitrogen-terminated aza-Prins pro-

cess, we investigated related reactions of N-acyloxy formal-

diminium ion intermediates. We initially examined initiating

the cyclization from N-cyanomethyl and N-benzotriazol-

methyl³⁹carbamates 37 and 39 (Scheme 6). At temperatures

up to 120 ꢀC, cyanomethyl derivative 37 was unchanged

when exposed to 2 equiv of AgO₂CCF₃, AgBF₄, or TsOH in

acetonitrile or toluene. Exposure of benzotriazole derivative

39 to 0.9 equiv of ZnBr₂in dichloromethane at 60 ꢀC initiated

aza-Prins cyclization to provide alkylidene decahydro-3,5-

ethanoquinoline products 40 in 63% yield. Other modes of

initiating the cyclization were also pursued;³⁹however, in no

case was any tetracyclic product detected.

(34) (a) Anderson, L. L.; Arnold, J.; Bergman, R. G. J. Am. Chem. Soc.

2005, 127, 14542–14543. (b) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37,

673–686.

We next turned to initiate the cyclization by acid-

promoted reaction of carbamate 38 with formaldehyde

(Scheme 7). Exposure of carbamate 38 to an excess of

paraformaldehyde in TFA/CHCl₃at room temperature^12b

resulted in formation of two inseparable tetracyclic products

41 whose molecular formulas (C₂₆H₃₆N₂O₄S, MS analysis)

indicated that 2 equiv of formaldehyde was involved in their

genesis. As these products were also produced upon expo-

sure of alkylidene decahydro-3,5-ethanoquinoline products

40 to identical conditions, they were assigned as the tetra-

cyclic alkene products of aza-Prins cyclization of N-sulfonyl-

formaldiminium ion intermediate 42. Using 1 equiv of

(35) Komeyama, K.; Morimoto, T.; Takaki, K. Angew. Chem., Int. Ed.

2006, 45, 2938–2941.

(36) See, inter alia: (a) Ziegler, F. E.; Spitzner, E. B. J. Am. Chem. Soc.

1973, 95, 7146–7149. (b) Stevens, R. V.; Lee, A. W. M. J. Am. Chem. Soc.

1979, 101, 7032–7035. (c) Overman, L. E.; Lesuisse, D.; Hashimoto, M.

J. Am. Chem. Soc. 1983, 105, 5373–5379.

(37) Anet, F. A. L.; Yavari, I. J. Am. Chem. Soc. 1977, 99, 2794–2796.

(38) In stereoelectronically more favorable contexts, regioselectivity of

deprotonation of this type in aza-Prins cyclizations can be ascribed to an ene

mechanism. For an early example, see: Kametani Tetrahedron Lett. 1986, 27,

1167–1170.

(39) (a) Katritzky, A. R.; Yao, G.; Lan, X.; Zhao, X. J. Org. Chem. 1993,

58, 2086–2093. (b) Kobayashi, S.; Ishitani, H.; Komiyama, S.; Oniciu, D. C.;

Katritzky, A. R. Tetrahedron Lett. 1996, 37, 3731–3734. (c) Katritzky, A. R.;

Pernak, J.; Fan, W.-Q. Synthesis 1991, 868–870. (d) Katritzky, A. R.; Fang,

Y.; Silina, A. J. Org. Chem. 1999, 64, 7622–7624.

J. Org. Chem. Vol. 75, No. 22, 2010 7523

Altman et al.

JOCFeatured Article

SCHEME 8. Elaboration of 27 to (()-5-epi-Nankakurine A (1)

paraformaldehyde, the tetracyclic product 27 resulting from

sulfonamide-terminated aza-Prins cyclization was formed,

albeit in low yield (10-20%). In this reaction, 27 was pro-

duced in a complex mixture of products that contained the

already characterized aza-Prins product 40 and tetracyclic

products 41. Much effort was expended in trying to optimize

the formation of spirocyclic product 27. Numerous varia-

tions in solvent, protic or Lewis acid, and formaldehyde pre-

cursor were surveyed, but no conditions were identified

under which 27 was formed in more than 20% yield.^40,41

Although the yield of the sulfonamide-terminated aza-

Prins reaction of bicyclic precursor 38 was low, this reaction

did provide sufficient quantities of tetracyclic diamine 27 to

allow the originally proposed structure of nankakurine A (1)

to be prepared in two additional steps (Scheme 8). Cleavage

of the sulfonamide of 27 by reaction with Na/NH₃provided

amino carbamate 43 in excellent yield. Lithium aluminum

hydride reduction of the methyl carbamate of this product

afforded (()-5-epi-nankakurine A (1) in 65% yield.

The NMR data for synthetic (()-1 did not match data

reported for nankakurine A.^2,42We considered it secure that

the tethered sulfonamide would undergo C-N bond forma-

tion to the cup-shaped decahydro-3,5-ethanoquinoline inter-

mediate (7, Scheme 1) from the less hindered convex face in

the sulfonamide-terminated aza-Prins reaction. With the

relative configuration at the spirocyclic stereocenter of pro-

duct 27 established, we hypothesized that the originally pro-

posed structure 1 for nankakurine A was incorrect. At

approximately the same time, Kobayashi and co-workers

reported that the relative configuration of nankakurine A at

the spiropiperidine stereocenter C5 should be reversed.⁴As

discussed earlier, this conclusion was founded on ¹H NMR

NOE studies of the conjugate acid of nankakurine B (3).

A serious complication in assigning the relative configura-

tion of the spiro stereocenter of nankakurines A and B

involved the existence of two conformational isomers of

the spiropiperidine ring, which made NOE measurements

difficult to interpret. Kobayashi and co-workers suggested

FIGURE 2. Molecular models of low-energy conformations of the

most stable disalts of nankakurine B 2; ΔE = E(conf B) - E(conf A)

in kcal/mol; energies marked with an asterisk refer to DFT calcula-

tions using the COSMO model for methanol solvent.

that this complication was responsible for the original mis-

assignment of the relative configuration of nankakurine A.⁴

This issue was proposed to be less serious for the disalt of

nankakurine B, which was suggested to exist predominantly

in conformer B on the basis of molecular mechanics calcula-

tions (Figure 2).⁴However, molecular modeling carried out

in our laboratory at the time did not support this conclusion

(B3-LYP/6-311G*), nor do more recent DFT calculations

using two functionals and higher-level basis sets.⁴³We

concluded that a definitive answer to the relative and abso-

lute configuration of the nankakurines would require their

total syntheses.

Synthesis of (þ)-Nankakurine A and (þ)-Nankakurine B.

A strategy for construction of structures (þ)-2 and (þ)-3

requires that the spiropiperidine nitrogen be located on the

concave face of the tricyclic decahydro-3,5-ethanoquinoline

moiety. We envisaged tetracyclic pyrazolidine 44, which

possesses the proper relative configuration at C5, as a logical

precursor to nankakurines A and B (Scheme 9). Pyrazolidine

44 was seen arising by an intramolecular dipolar cycloaddi-

tion of azomethine imine 45.⁴⁴High regioselection in this

step was anticipated based on the prospect that C-C bond

formation would be more advanced than C-N bond forma-

tion,^44aan expectation bolstered by the high regioselectivity

observed in Oppolzer’s construction of (þ)-luciduline by

intramolecular cycloaddition of an analogous nitrone

intermediate.¹³Hydrazine 6 would readily derive from octa-

hydronaphthalene ketone 47.

In a sequence analogous to that employed for the synthesis

of 5-epi-nankakurine A (1), octahydronaphthalenone 50

was constructed in enantioenriched form by the cationic

Diels-Alder reaction of (R)-5-methyl-2-cyclohexen-1-one

((þ)-9) and 2-substituted-1,3-butadiene 48 (Scheme 10).

Diene 48 was available in two high-yielding steps from

(40) The yield was similar in CHCl₃alone. Although AcOH promoted the

desired reaction in 12% yield, reactions employing other acids such as

camphorsulfonic acid, methanesulfonic acid, and formic acid did not afford

any of the tetracyclic product 27. Moreover, the desired spirotetracyclic

product was not detected when TFA was employed neat or as a solution in

THF, MeOH, DMF, PhMe, or H₂O. The use of Lewis acids, such as

BF₃•OEt₂, TiCl₄, SnCl₄, AlCl₃, FeCl₃, CeCl₃, or TMSOTf at -65 ꢀC to

room temperature in CH₂Cl₂did not provide any detectable 27. The use of

formalin or 1,3,5-trioxane instead of formaldehyde under various conditions

also did not lead to 27.

(43) (a) The TURBOMOLE V6.2 quantum chemistry program was

utilized for higher-level DFT calculations: TURBOMOLE V6.2; Turbomole

GmbH: Karlsruhe, Germany, 2009; http://www.turbomole.com. (b) Treutler,

O.; Ahlrichs, R. J. Chem. Phys. 1995, 102, 346–354.

(44) For a recent review, see: (a) Schantl, J. G. Azomethine Imines.

Science of Synthesis; Georg Thieme Verlag: Stuttgart, Germany, 2004; Vol.

27, p 731. For select examples, see: (b) Oppolzer, W. Tetrahedron Lett. 1970,

11, 3091–3094. (c) Oppolzer, W. Tetrahedron Lett. 1972, 13, 1707–1710.

(d) Oppolzer, W. Angew. Chem., Int. Ed. Engl. 1977, 16, 10–23. (e) Jacobi,

P. A.; Martinelli, M. J.; Polanc., S. J. Am. Chem. Soc. 1984, 106, 5594–5598.

(f) Katz, J. D.; Overman, L. E. Tetrahedron 2004, 60, 9559–9568. (g) Gergely,

J.; Morgan, J. B.; Overman, L. E. J. Org. Chem. 2006, 71, 9144–9152.

(41) We do not attribute the low yield of 27, in an appreciable extent, to its

instability under acidic conditions. Although 27 fragments slowly to a

mixture of tricyclic alkenes 40 in the presence of 10 equiv of TFA in CDCl₃

at rt, its half-life under these conditions was ∼5 h.

(42) After eventually completing the synthesis of authentic nankakurine

A (2), we became convinced that the spectra in the original report were

obtained from a natural sample that contained a mixture of the free base and

its conjugate acid (vide infra). As a result, ¹H NMR spectra of various

mixtures of synthetic (()-1 and its trifluoroacetate salt were measured. None

of these spectra matched the ¹H NMR data reported for natural nankakurine

A (see data in the Supporting Information).²

7524 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

SCHEME 9. Retrosynthetic Analysis of (þ)-Nankakurines

A (2) and B (3)

TABLE 1. Dipolar Cycloaddition of Unsaturated Hydrazine Deriva-

tives 51-53

entry

R

solvent^a

additive

yield (%) 54

1

2

3

4

5

6

7

CO₂Me

Ts

Bz

CHCl₃

PhMe

CHCl₃

PhMe

CHCl₃

PhMe

TFA (20 equiv)

˚

4 A mol sieves

TFA (20 equiv)

˚

4 A mol sieves

TFA (20 equiv)

˚

4 A mol sieves

Et₃N

˚

4 A mol sieves

i-Pr₂NEt

˚

4 A mol sieves

0

Bz

40

80^b

SCHEME 10. Synthesis of cis-Octahydronaphthalene Hydra-

zine Derivatives 51-53

8

Bz

PhMe

85^c

^aReactions run in CHCl₃at rt or PhMe at 120 ꢀC. ^bAfter 24 h. ^cAfter

5 h.

unactivated trisubstituted alkenes were to our knowledge

unknown. As a result, we anticipated that the electron-

withdrawing substituent on the dipole might need to be

finely tuned for the projected cycloaddition to succeed.^44a,g

Hydrazine derivatives carrying carbomethoxy, p-toluenesul-

fonyl, and benzoyl groups were prepared in varying yields by

hydrazone formation, followed by reaction with sodium

cyanoborohydride, the reduction occurring exclusively from

the convex β-face to deliver 51-53.⁴⁸In order to avoid

partial epimerization adjacent to the ketone, it was essential

that the hydrazone intermediate was prepared under neutral

conditions.

The pivotal intramolecular dipolar cycloaddition was

surveyed under both thermal and acidic conditions. In

preliminary studies, hydrazines 51-53 were allowed to react

with excess (CH₂O)_neither in refluxing toluene in the pre-

5-hexyn-1-ol (16): benzyl protection,⁴⁵followed by enyne

cross metathesis with ethylene using Grubbs’ second genera-

tion catalyst.^22,23Cyclohexenone (þ)-9 (>99% ee) was pre-

pared from (þ)-pulegone (49) in four steps by a known,

efficient sequence.⁴⁶Allowing diene 48, cyclohexenone (þ)-

9, and 1,2-bis(trimethylsiloxy)ethane to react in CH₂Cl₂at

-78 ꢀC in the presence of 10 mol % of TMSOTf,²⁵followed

by cleavage of the dioxolane with FeCl₃adsorbed on silica

gel,²⁶gave cis-octahydroquinolone 50 in 67% yield as a

single stereoisomer.⁴⁷

˚

sence of 4 A molecular sieves or at room temperature in

CHCl₃in the presence of 20 equiv of TFA (Table 1). With the

carbamate and sulfonamide precursors, only the octahydro-

3,5-ethanoquinoline aza-Prins products 55 were produced

(entries 1-4). Although acidic conditions were not successful

(entry 5), reaction of benzoylhydrazide 53 with (CH₂O)_nand

˚

4 A molecular sieves in refluxing toluene provided the

tetracyclic pyrazolidine product 54 in 40% yield together

with aza-Prins products 55 (entry 6).⁴⁹Carrying out this

reaction in the presence of basic additives provided dipolar

cycloaddition product 54 in 80-85% yield, with the reaction

being slightly faster in the presence of diisopropylethylamine

than triethylamine (entries 7 and 8).

Intramolecular or bimolecular dipolar cycloadditions

of azomethine imines derived from formaldehyde with

Our interpretation of the positive effect of basic additives

on the efficiency of the pivotal intramolecular dipolar cyclo-

addition is outlined in Scheme 11. Dehydrative condensation

(45) (a) Takami, K.; Mikami, S.; Yorimitsu, H.; Shinokubo, H.; Oshima,

K. J. Org. Chem. 2003, 68, 6627–6631.

(46) Fleming, I.; Maiti, P.; Ramarao, C. Org. Biomol. Chem. 2003, 1,

3989–4004, and references therein

(47) The Diels-Alder reaction of enone (þ)-9 and diene 48 and subse-

quent deprotection to prepare 50 was performed prior to the finding that the

Diels-Alder reaction of (()-15 with 19, followed by deprotection provided a

higher yield of the cis-octahydronaphthalene ketone. It would be expected

that the Diels-Alder reaction of (þ)-15 with 48 would increase the yield of 50

obtained after deprotection.

(48) Hydrazines 51 and 52 were prepared only once; no attempt was made

to optimize their syntheses.

(49) The structure of 54 was confirmed by single-crystal X-ray analysis:

CCDC 690534. These data can be obtained free of charge from The Cambridge

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

J. Org. Chem. Vol. 75, No. 22, 2010 7525

Altman et al.

JOCFeatured Article

SCHEME 11. Competition between Intramolecular Azo-

methine Imine Dipolar Cycloaddition and Aza-Prins Cyclization

reduction of the amide with aluminum hydride,⁵²provided

diamine alcohol 60 in 72% yield. Selective O-mesylation of

this intermediate at -40 ꢀC followed by warming the primary

mesylate to ambient temperature generated the spiropiper-

idine ring and furnished N-benzylnankakurine A (61) in 96%

yield.⁵³Hydrogenolysis of this intermediate in acidic metha-

nol then gave (þ)-nankakurine A (2), [R]²⁴þ13 (c 0.4,

D

MeOH), in 99% yield. Standard reductive methylation of

nankakurine A (2) delivered (þ)-nankakurine B (3), [R]²⁴

D

þ12 (c 1.5, MeOH), in 80% yield.⁵⁴

The ¹H NMR spectra of synthetic 2 and 3 did not initially

match those reported for the natural products (Figure 3).

Because basic nitrogen atoms readily protonate, we were

able to reproducibly obtain ¹H and ¹³C NMR spectra of the

free base forms of nankakurines A (2) and B (3) only in

CD₃OD containing a trace amount of NaOCD₃. These

spectra were not identical to those reported for natural 2

and 3 in CD₃OD.⁴We surmised that the natural isolates

contained unknown amounts of their conjugate acids. Thus,

SCHEME 12. Completion of the Enantioselective Total Synthe-

ses of (þ)-Nankakurine A (2) and (þ)-Nankakurine B (3)

1

we examined the H NMR spectra of synthetic (þ)-nanka-

kurine A (2) and (þ)-nankakurine B (3) by titrating samples

1

of the free bases with TFA. As reproduced in Figure 3, H

NMR spectra identical to those of the natural products were

obtained. These data are consistent with the notion that the

natural samples contained an undetermined amount of the

conjugate acids.

Evaluation of the Neurotrophic Properties of (þ)-Nankak-

urine A (2) and (þ)-Nankakurine B (3). The purported

neurotrophic properties of (þ)-nankakurine A (2) and (þ)-

nankakurine B (3) were investigated in the following fashion.

Immortalized embryonic rat hippocampus H19-7 cells were

grown in the presence of N-2 supplement medium. After

24 h, cells were treated with either 2 or 3. After an additional

24 h, the cells were fixed and incubated successively with an

antibody against neuronal class III β-tubulin and a second-

ary Alexa Fluor 546 goat anti-mouse antibody. After stain-

ing, the length of neurites and the cell count were quantified

using fluorescence microscopy.^55,56Neither (þ)-nankak-

urine A nor (þ)-nankakurine B increased neurite outgrowth

over a concentration range of 0.3-10 μM (Figure 4), nor did

they display any toxicity or change in cell number. Under the

same conditions, a positive reference compound increased

neurite outgrowth by 60% at 1.0 μM.

of benzoylhydrazide 53 with paraformaldehyde generates

azomethine imine 56, which undergoes intramolecular cyclo-

addition to yield cycloadduct 54. In the absence of a basic

additive, the efficiency of this reaction is undermined by

protonation of 56 by adventitious acid (likely formic acid) to

generate N-benzamidoformaldiminium ion 57, which under-

goes aza-Prins cyclization to give octahydro-3,5-ethano-

quinoline 55 via tertiary carbenium ion intermediate 58. In

the presence of base, iminium electrophile 57 is not generated.⁵⁰

The total syntheses of (þ)-nankakurine A (2) and (þ)-

nankakurine B (3) were concluded in five and six steps,

respectively, from cycloadduct 54 (Scheme 12). Cleavage of

the N-N bond with SmI₂⁵¹and selective reductive methyla-

tion of the secondary amine product afforded diamine 59 in

80% overall yield in this one-pot sequence. Hydrogenolytic

cleavage of the O-benzyl protecting group, followed by

Conclusions

In summary, the first total syntheses of (þ)-nankakurine A

(2), (þ)-nankakurine B (3), and the originally proposed struc-

ture of nankakurine A (1, 5-epi-nankakurine A) were accom-

plished. Pivotal steps in these syntheses include the first

example of a dipolar cycloaddition of an azomethine imine

derived from formaldehyde with an unactivated trisubstituted

alkene and a nitrogen-terminated aza-Prins cyclization. The

total syntheses of (þ)-2 and (þ)-3, together with the synthesis

of the originally purported structure 1 of nankakurine A,

(52) Brown, H. C.; Yoon, N. M. J. Am. Chem. Soc. 1966, 88, 1464–1472.

(53) To facilitate monitoring reactions and purifying intermediates, the

N-benzyl protecting group was retained until the last step.

(54) Reported optical rotations for the natural products are: (a) nankak-

urine A: [R]²¹_Dþ16 (c 0.4, MeOH);²(b) nankakurine B: [R]¹⁹_Dþ12 (c 1.0,

MeOH).⁴

(55) Eves, E. M.; Tucker, M. S.; Roback, J.; Downen, M.; Rosner, M. R.

Proc. Natl. Acad. Sci. U.S.A. 1992, 89, 4373–4377.

(56) Representative images can be found in the Supporting Information.

(50) For enhancement of yields using Et₃N in bimolecular cycloadditions

of formaldehyde-derived azomethine imines, see: Kanemasa, S.; Tomoshige,

N.; Wada, E.; Tsuge, O. Bull. Chem. Soc. Jpn. 1989, 62, 3944–3949.

(51) Freshly prepared SmI₂was required to obtain reproducible yields for

this reaction.

7526 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

FIGURE 3. ¹H NMR spectra of the titration of synthetic (þ)-2 and (þ)-3 with TFA. (a) Matches ¹H NMR of 2 reported in 2004.²(b) Matches

¹H NMR of 3 reported in 2006.⁴

FIGURE 4. Absence of neurotrophic properties of (þ)-nankakurine A (2) and (þ)-nankakurine B (3) in rat hippocampus cells; data are

expressed as the mean of two separate experiments; control = DMSO; reference = positive reference compound.

rigorously establish the relative and absolute configuration of

these Lycopodium alkaloids. These syntheses were sufficiently

concise that substantial quantities of these alkaloids could be

prepared for biological evaluation. (þ)-Nankakurine A (2) and

(þ)-nankakurine B (3) showed no effect on neurite outgrowth

in rat hippocampus H-19 cells over a concentration range of

0.3-10 μM, which stands in contrast to the report of neuro-

trophic activity of the former in human astrocytoma cells.²

of nitrogen using anhydrous solvents. THF, DMF, CH₂Cl₂,

PhMe, MeOH, MeCN, Et₂O, Et₃N, and i-Pr₂NEt were passed

through activated alumina columns.⁵⁷CHCl₃was distilled from

58

˚

Na₂SO₄and stored over 4 A molecular sieves. EtOH (200

proof) and acetone (ACS grade) were purchased from commer-

cial sources and used without further purification. FeCl₃/silica²⁶

and AlH₃were prepared as previously described. SmI₂

was freshly prepared prior to each usage. Trimethylsilyl triflate

52

51,59

was distilled from CaH₂.⁵⁸Methyl chloroformate was distilled

Experimental Section

(57) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;

Timmers, F. J. Organometallics 1996, 15, 1518.

(58) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory

Chemicals, 5th ed; Butterworth Heinemann: Amsterdam, 2003.

Materials and Methods. Unless stated otherwise, reactions

were conducted in flame-dried glassware under an atmosphere

J. Org. Chem. Vol. 75, No. 22, 2010 7527

Altman et al.

JOCFeatured Article

from CaCl₂.⁵⁸All other commercially obtained reagents were

used as received. Reaction temperatures were controlled using a

temperature modulator, and unless stated otherwise, reactions

were performed at room temperature (rt, approximately 25 ꢀC).

Thin-layer chromatography (TLC) was conducted with silica

gel 60 F₂₅₄precoated plates (0.25 mm) and visualized by ex-

posure to UV light (254 nm) or stained with anisaldehyde, ceric

ammonium molybdate, potassium permanganate, or iodide.

Flash column chromatography was performed using normal

J = 6.5 Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 204.2,

192.6, 104.0, 48.2, 40.7, 29.0, 21.0 ppm.

3-Bromo-5-methylcyclohex-2-enone (14). Following a known

procedure,¹⁷oxalyl bromide (22 mL, 240 mmol) was added

dropwise over 20 min (CAUTION gas evolution) to a solution

of diketone 13 (25.0 g, 198 mmol), DMF (20 mL, 260 mmol),

and CH₂Cl₂(500 mL) at 0 ꢀC. The reaction was stirred at 0 ꢀC

for 15 min, allowed to warm to rt, and stirred for 1 h at rt, after

which H₂O (500 mL) was added, and the biphasic mixture was

stirred for 1 h. The layers were separated, and the aqueous layer

was extracted with CH₂Cl₂(500 mL). The combined organic

layers were washed with brine (500 mL), dried with MgSO₄, and

concentrated in vacuo. The residue was purified by flash chro-

matography (hexanes/EtOAc 1:0f3:1) to provide 14^17aas a

yellow oil (35.2 g, 94%): ¹H NMR (500 MHz, CDCl₃) δ 6.46 (s,

1H), 2.86 (dd, J = 4.7, 18.5 Hz, 1H), 2.51 (m, 1H), 2.46 (d, J =

4.0 Hz, 1H), 2.37-2.30 (m, 1H), 2.10 (dd, 1H, J = 12.0, 16.3

Hz), 1.10 (d, 3H, J = 6.7 Hz) ppm; ¹³C NMR (125 MHz,

CDCl₃) δ 196.7, 149.6, 132.4, 44.8, 44.5, 30.8, 20.8 ppm.

5-Methylcyclohex-2-enone [(()-9]. A 1 L three-neck round-

bottom flask was charged with Zn⁰(37 g, 580 mmol, washed

with AcOH and dried), 1,2-dibromoethane (6.2 mL, 72 mmol),

and THF (200 mL), and the slurry was stirred and heated with a

heat gun until ethylene gas evolved (CAUTION gas evolution).

The slurry was allowed to cool to rt. The heating/cooling cycle

was repeated two additional times. A solution of 14 (27.2 g, 144

mmol) in THF (200 mL) was added to the reaction mixture at a

rate that maintained the reaction temperature at <35 ꢀC. The

reaction was stirred at rt for 24 h and then quenched by the

addition of saturated aqueous NH₄Cl (300 mL). The aqueous

layer was extracted with CH₂Cl₂(3ꢀ100 mL), and the com-

bined organic extracts were dried with MgSO₄and concen-

trated. Purification by flash chromatography (hexanes/EtOAc

0:1f1:1) provided enone (()-9⁶³as a pale yellow oil (14.2 g,

94%): ¹H NMR (500 MHz, CDCl₃) δ 6.95 (ddd, J = 2.6, 5.5,

10.0 Hz, 1H), 6.01 (dd, J = 1.4, 10.1 Hz, 1H), 2.48 (dd, J = 2.6,

16.0 Hz, 1H), 2.42 (dt, J = 5.4, 18.6 Hz, 1H), 2.29-2.17 (m, 1H),

2.12 (dd, J = 12.3, 15.8 Hz, 1H), 2.04 (ddt, J = 2.7, 9.8, 18.5 Hz,

1H), 1.07 (d, J = 6.6 Hz, 3H) ppm; ¹³C NMR (125 MHz,

CDCl₃) δ 200.3, 150.1, 129.8, 46.5, 34.2, 30.5, 21.4 ppm; IR (thin

˚

phase silica gel (60 A, 230-240 mesh).

¹H NMR spectra were recorded on 500 or 600 MHz spectro-

meters and are reported relative to deuterated solvent signals.

Data for ¹H NMR spectra are reported as follows: chemical shift

(δ ppm), multiplicity, coupling constant (Hz), and integration.

¹³C NMR spectra were recorded at 125 or 150 MHz. Data for

¹³C NMR spectra are reported in terms of chemical shift (δ

ppm). IR spectra were recorded on a spectrometer and are

reported in terms of frequency of absorption (cm^-1). Optical

rotations were measured with a polarimeter. High-resolution

mass spectra were obtained using the electrospray ionization

method.

Experimental Procedures. 1,3-Dimethoxy-5-methylbenzene

(12). Orcinol (11, 25.0 g, 0.202 mol) was heated at reflux with

MeI (62 mL, 1.0 mol) and anhydrous K₂CO₃(140 g, 1.0 mol) in

acetone (500 mL) overnight. After cooling to rt, the reaction

mixture was filtered through diatomaceous earth, and the

filtrate was concentrated in vacuo. Chromatographic purifica-

tion of the residue (hexanes/EtOAc 19:1) provided 12⁶⁰as a clear

oil (27 g, 89%): ¹H NMR (500 MHz, CDCl₃) δ 6.35 (d, J = 2.1

Hz, 2H), 6.31 (t, J = 2.2 Hz, 1H), 3.80, (s, 6H), 2.32 (s, 3H) ppm;

¹³C NMR (125 MHz, CDCl₃) δ 160.9, 140.4, 107.3, 97.7, 66.1,

55.4, 22.0 ppm.

1,5-Dimethoxy-3-methylcyclohexa-1,4-diene (S1). A solution

of 12 (760 mg, 5.0 mmol) in anhydrous EtOH (5.0 mL) was

added dropwise over 10 min to a solution of Li⁰(350 mg, 0.050

mol) and NH₃(50 mL) at -50 ꢀC. The reaction mixture was

stirred at -50 ꢀC for 1 h, then quenched by the addition of

saturated aqueous NH₄Cl (10 mL) and warmed to rt. The

aqueous mixture was extracted with hexanes (3ꢀ10 mL). The

combined extracts were dried with MgSO₄and concentrated in

film) 1681, 1457, 1390, 879, 734 cm^-1

.

vacuo to provide S1⁶¹as a clear oil (650 mg, 85%): H NMR

1

9-Methyl-1,4-dioxaspiro[4.5]dec-6-ene (15). An oven-dried

Schlenk tube was charged with (()-9 (12.1 g, 110 mmol) and

1,2-bis(trimethylsiloxy)ethane (27 mL, 0.10 mmol), evacuated,

and backfilled with N₂. Dichloromethane (8.0 mL) was added,

the solution was cooled to -78 ꢀC, and TMSOTf (360 μL, 2.0

mmol) was added dropwise. The reaction vessel was sealed, and

the reaction mixture was stirred at -78 ꢀC for 23 h. The reaction

mixture was quenched by the addition of NEt₃(2 mL), warmed

to rt, and filtered through a plug of basic Al₂O₃. The plug was

rinsed with excess Et₂O (50 mL), and the volatiles were removed

in vacuo. Purification of the residue by flash chromatography

(hexanes/Et₂O/NEt₃99:0:1f90:10:1) provided ketal 15¹⁸as a

pale yellow oil (12.3 g, 73%) along with recovered (()-9 (3.5 g,

30%); ketal 15: ¹H NMR (500 MHz, CDCl₃) δ 5.95 (ddd, J =

2.2, 5.2, 10.0 Hz, 1H), 5.60-5.57 (m, 1H), 4.07-3.83 (m, 4H),

2.14 (dt, J = 5.1, 17.8 Hz, 1H), 2.01-1.93 (m, 1H), 1.88-1.84

(m, 1H), 1.65(ddt, J= 2.5, 10.7, 17.8 Hz, 1H), 1.48 (t, J= 13.0 Hz,

1H), 1.00 (d, J= 6.6 Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ

132.5, 127.3, 106.7, 64.8, 64.5, 42.2, 38.8, 28.1, 21.8 ppm.

(500 MHz, CDCl₃) δ 4.58 (dt, J = 1.2, 3.5 Hz, 2H), 3.57 (s, 6H),

3.05 (1H, m), 2.77 (dq, J = 1.1, 6.7 Hz, 2H), 1.09 (d, J = 7.0 Hz,

3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 151.4, 98.0, 54.3, 31.3,

30.9, 24.7 ppm.

5-Methylcyclohexane-1,3-dione (13). Cyclohexadiene S1 (650

mg, 4.2 mmol) was stirred in 1 M HCl (5 mL) and THF (50 mL)

overnight at rt and then concentrated in vacuo. The aqueous

layer was extracted with CH₂Cl₂(3 ꢀ 10 mL), and the combined

organic extracts were dried with MgSO₄. The solvent was

removed in vacuo to provide 13⁶²as a colorless solid (440 mg,

83%, a 5:1 mixture of hydroxyenone-diketone tautomers): ¹H

NMR (500 MHz, CDCl₃, 3-hydroxyenone tautomer) δ 11.30,

(br s, 1H), 5.47 (s, 1H), 2.43 (dd, J = 4.3, 17.0 Hz, 2H),

2.29-2.20 (m, 1H), 2.10 (dd, J = 11.1, 17.0 Hz, 2H), 1.08 (d,

(59) Samarium metal (5.64 g, 37.5 mmol, 40 mesh) was transferred into a

Schlenk flask in a glovebox. The Schlenk flask was sealed, removed from the

glovebox, and placed under a steady stream of nitrogen. A solution of iodine

(6.35 g, 25.0 mmol) in THF (250 mL, freshly distilled from a ketyl still) was

transferred by cannula to the Schlenk flask. Upon completion of the cannula

transfer, the Schlenk tube was sealed under nitrogen and heated to 50 ꢀC for

24 h. The reaction mixture was cooled to rt, and the dark blue stock solution

of SmI₂(∼0.08 M) was used without further purification.

Hex-5-yn-1-amine Hydrochloride (16). A solution of 17

(25.0 g, 255 mmol) and diisopropyl azodicarboxylate (51 mL,

260 mmol) in THF (160 mL) was added by cannula at 0 ꢀC to a

solution of PPh₃(66.8 g, 255 mmol) and phthalimide (37.5 g, 255

mmol) in THF (330 mL) over 20 min. The clear yellow solution

(60) (a) Mondal, M.; Puranik, 4V. G.; Argade, N. P. J. Org. Chem. 2007,

72, 2068–2076. (b) Tietze, L. E.; Spiegl, D. A.; Stecker, F.; Major, J.; Raith,

C.; Grosse, C. Chem.;Eur. J. 2008, 14, 8956–8963.

(61) Clark, R. S. J.; Holmes, A. B.; Matassa, V. G. J. Chem. Soc., Perkin

Trans. 1 1990, 1389–1400.

(62) Musser, A. K.; Fuchs, P. L. J. Org. Chem. 1982, 47, 3121–3131.

(63) Watson, I. D. G.; Yudin, A. K. J. Am. Chem. Soc. 2005, 127, 17516–

17429.

7528 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

was allowed to warm to rt overnight. Hydrazine hydrate (20 mL,

51 wt %, 306 mmol) was added, and the resulting solution was

heated at reflux for 6 h. The solution was allowed to cool to rt,

and concentrated HCl (50 mL) was slowly added. The solution

was refluxed for 2 h, then allowed to cool to rt, and stirred

overnight. The colorless precipitate (PPh₃O) was removed by

filtration, and the eluent was removed in vacuo. The residual

colorless solid was redissolved in H₂O (500 mL) and extracted

with CH₂Cl₂(3 ꢀ 500 mL). The aqueous layer was concentrated

and TMSOTf (420 μL, 2.3 mmol) was added dropwise. The tube

was sealed and stirred at -78 ꢀC for 20 h. The reaction mixture

was quenched at -78 ꢀC by the addition of NEt₃(2 mL) and

warmed to rt. The mixture was diluted with 20 mL of Et₂O,

filtered through a short silica gel column, and the eluent was

concentrated in vacuo to afford S2 as a yellow oil.

Ketal S2 was dissolved in acetone (80 mL) and stirred at rt for

4 h with FeCl₃/SiO₂(1.3 g).²⁶Silica gel (50 g) was added, and the

solvent was removed in vacuo. Purification of the residue by

flash chromatography (dry packed, hexanes/Et₂O 9:2f1:2)

provided 20 as a yellow oil (9.07 g, 93%): ¹H NMR (500

MHz, CDCl₃) δ 7.71 (d, J = 8.0 Hz, 2H), 7.25 (d, J =

8.5 Hz, 2H), 5.19 (br s, 1H), 5.14 (t, J = 6.0 Hz, 1H), 2.83 (q,

J = 6.5 Hz, 2H), 2.61 (t, J = 5.5 Hz, 1H), 2.44-2.39 (m, 1H),

2.37 (s, 3H), 2.34-2.29 (m, 1H), 2.16-2.12 (m, 1H), 2.09-2.04

(m, 2H), 1,97-1.90 (m, 2H), 1.87-1.74 (m, 3H), 1.68-1.59 (m,

2H), 1.40-1.35 (m, 2H), 1.34-1.26 (m, 2H), 0.97 (d, J = 6.5 Hz,

3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 211.9, 143.1, 137.1,

134.9, 129.6, 127.1, 118.8, 49.6, 47.0, 43.1, 38.4, 36.9, 35.6, 30.7,

29.8, 28.7, 24.2, 23.6, 22.5, 21.5 ppm; IR (thin film) 3286, 2915,

1702, 1599, 1325, 1160, 1095, 905 cm^-1; HRMS (ESI) m/z

412.1929 (412.1922 calcd for C₂₂H₃₁NO₃SNa^þ[MNa]^þ).

(E)-N-(4-(5-(Hydroxyimino)-7-methyl-1,4,4a,5,6,7,8,8a-octa-

hydronaphthalen-2-yl)butyl)-4-methylbenzenesulfonamide (21).

Aqueous H₂NOH (6.2 mL, 94 mmol, 50 wt %) was added over 5

min to a stirred solution of ketone 20 (9.07 g, 23.2 mmol) in

MeOH (250 mL) at rt. The reaction was stirred for 4 h, and the

solvent was removed in vacuo. The residue was partitioned

between CH₂Cl₂(150 mL) and saturated aqueous NH₄Cl

(100 mL). The layers were separated, and the aqueous layer

was extracted with CH₂Cl₂(2 ꢀ 100 mL); the combined organic

layers were dried with MgSO₄and concentrated to provide the

cis-oxime as a colorless solid (9.24 g, 99%): ¹H NMR (500 MHz,

CDCl₃) δ 8.52 (br s, 1 H), 7.77 (d, J = 8 Hz, 2H), 7.31 (d, J = 7.5

Hz, 2H), 5.23 (s, 1H), 4.75 (br s, 1H), 3.21 (dd, J = 13, 3.5 Hz,

1H), 2.93-2.91 (m, 2H), 2.51-2.50 (m, 1H), 2.44 (s, 3H),

2.42-2.38 (m, 1H), 2.22-2.18 (m, 1H), 2.09-2.05 (m, 1H),

2.01-1.96 (m, 1H), 1.88-1.84 (m, 2H), 1.83-1.79 (m, 1H),

1.71-1.68 (m, 2H), 1.52 (dd, J = 13.5, 11 Hz, 1H), 1.44-1.39

1

to provide 16⁶⁴as an off-white solid (32.8 g, 97%): H NMR

(500 MHz, CD₃OD) δ 2.96 (t, J = 7.6 Hz, 2H), 2.29-2.24 (m,

3H), 1.79 (m, 2H), 1.64-1.57 (m, 2H) ppm; ¹³C NMR (125

MHz, CDCl₃) δ 84.2, 70.5, 40.5, 27.8, 26.5, 18.7 ppm. This

ammonium salt was used in the subsequent step without further

purification.

N-(Hex-5-ynyl)-4-methylbenzenesulfonamide (18). p-Toluene-

sulfonyl chloride (12.6 g, 65.9 mmol) was added in four por-

tions over 30 min to a solution of ammonium salt 17 (8.00

59.9 mmol), NEt₃(25 mL, 180 mmol), and CH₂Cl₂(120 mL) at

0 ꢀC. The reaction was allowed to warm to rt and stirred

overnight. The reaction was quenched with saturated aqueous

NH₄Cl and extracted with CH₂Cl₂(3 ꢀ 150 mL). The combined

organic layers were dried with MgSO₄and concentrated in

vacuo. The residue was purified by column chromatography

(hexanes/EtOAc 1:0f3:2) to afford sulfonamide 18⁶⁵as a

colorless solid (12.6 g, 85%): mp 63-65 ꢀC; ¹H NMR (500

MHz, CDCl₃) δ 7.75 (d, J = 8.5 Hz, 2H), 7.30 (d, J = 8 Hz, 2H),

4.95-4.88 (m, 1H), 2.94 (q, J = 6.5 Hz, 2H), 2.42 (s, 3H),

2.15-2.12 (m, 2H), 1.91 (t, J = 2.5 Hz, 1H), 1.61-1.55 (m,

2H), 1.51-1.47 (m, 2H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ

143.5, 137.1, 129.9, 127.2, 83.9, 69.0, 42.8, 28.6, 25.4, 21.7, 18.0

ppm; IR (thin film) 3294, 2944, 2870, 1598, 1426, 1322, 1154,

1092 cm^-1; HRMS (ESI) m/z 274.0871 (274.0878 calcd for

C₁₃H₁₇NO₂SNa^þ[MNa]^þ).

4-Methyl-N-(5-methylenehept-6-enyl) Benzenesulfonamide (19).

A solution of alkyne 18 (1.5 g, 5.9 mmol) and CH₂Cl₂(100 mL)

was degassed by sparging with nitrogen for 30 min. Benzylidene-

[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro

(tricyclohexylphosphine)ruthenium (0.18 g, 0.21 mmol)²²was

added to the degassed solution, and the mixture was charged to a

high-pressure bomb. The reaction bomb was filled with ethylene

gas (300 psi), vented, and repressurized with ethylene (300 psi).

This process was repeated a total of three times. The reaction

was stirred at rt under high pressure (300 psi) for 4-5 h. After

venting unreacted ethylene, the reaction mixture was transferred

to a round-bottom flask containing silica gel and the solvent was

removed in vacuo. The residue was purified by column chro-

matography (dry load, hexanes/EtOAc 4:1) to give diene 19

(1.5 g, 90%) as a tan oil: ¹H NMR (500 MHz, CDCl₃) δ 7.76 (d,

J = 8.5 Hz, 2H), 7.28 (d, J = 8 Hz, 2H), 6.30 (dd, J = 17.5, 10.5

Hz, 1H), 5.25 (t, J = 6 Hz, 1H), 5.14 (d, J = 18 Hz, 1H), 5.00 (d,

J = 11 Hz, 1H), 4.95 (s, 1H), 4.88 (s, 1H), 2.92 (q, J = 6 Hz, 2H),

(m, 2H), 1.38-1.35 (m, 3H), 1.01 (d, J = 6.5 Hz, 3H) ppm; ¹³

C

NMR (125 MHz, CDCl₃) δ 160.2, 143.4, 137.4, 135.4, 129.8,

127.3, 119.2, 42.9, 39.6, 38.4, 36.9, 34.5, 32.0, 30.1, 28.9, 28.6,

25.8, 23.8, 22.3, 21.7 ppm; IR (thin film) 3286, 2907, 1597, 1458,

1446, 1323, 1156, 1092 cm^-1; HRMS (ESI) m/z 427.2025

(427.2031 calcd for C₂₂H₃₂N₂O₃SNa^þ[MNa]^þ).

N-(4-(-5-Amino-7-methyl-1,4,4a,5,6,7,8,8a-octahydronapht-

halen-2-yl)butyl)-4-methylbenzenesulfonamide (22). cis-Oxime

21 (4.04 g, 10.0 mmol) was dissolved in EtOH (250 mL) and

stirred at 30-35 ꢀC. MoO₃(1.9 g, 13 mmol) was added followed

by NaBH₄(1.9 g, 50 mmol; CAUTION gas evolution), and the

reaction was stirred for 1 h, during which the solution turned

brown. A second portion of MoO₃(1.9 g, 13 mmol) and NaBH₄

(1.9 g, 50 mmol) was added, and the reaction was stirred for an

additional 1 h. A third portion of MoO₃(1.9 g, 13 mmol) and

NaBH₄(1.9 g, 50 mmol) was added, and the reaction was stirred

for an additional 1 h. The reaction mixture was cooled to rt, and

a solution of KOH_(aq)(0.2 M, 50 mL) was added. The slurry was

stirred for 2 h. The brown precipitate was filtered with diato-

maceous earth, and the filter cake was washed with excess

methanol (300 mL). The filtrate was concentrated in vacuo.

The residue was dissolved in saturated aqueous NH₄Cl (150 mL)

and extracted with CH₂Cl₂(4 ꢀ 100 mL). The combined organic

layers were dried with MgSO₄and concentrated to provide the

amine as a colorless solid that was used without further puri-

fication (3.52 g, 90%): ¹H NMR (500 MHz, CDCl₃) δ 7.72 (d,

J = 8.0 Hz, 2H), 7.25 (d, J = 8.0 Hz, 2H), 5.23 (s, 1H), 3.61 (br s,

2H), 3.13 (br s, 1H), 2.85 (t, J = 6.5, Hz, 2H), 2.38 (s, 3H),

2.10-2.06 (m, 2H), 1.99-1.85 (m, 4H), 1.81 (t, J = 7.5 Hz, 2H),

2.40 (s, 3H), 2.11 (t, J = 7 Hz, 2H), 1.49-1.43 (m, 4H) ppm; ¹³

C

NMR (125 MHz, CDCl₃) δ 145.8, 143.3, 138.7, 137.1, 129.7,

127.1, 115.8, 113.3, 43.1, 30.7, 29.3, 25.0, 21.5 ppm; IR (thin

film) 3299, 2929, 1325, 1160, 1094 cm^-1; HRMS (ESI) m/z

302.1186 (302.1191 calcd for C₁₅H₂₁NO₂SNa^þ[MNa]^þ).

4-Methyl-N-(4-(7-methyl-5-oxo-1,4,4a,5,6,7,8,8a-octahydro-

naphthalen-2-yl)butyl)benzenesulfonamide (20). An oven-dried

Schlenk tube was charged with 15 (5.7 g, 37 mmol) and 19 (6.9 g,

25 mmol), evacuated and backfilled with Ar. Dichloromethane

(25 mL) was added, the reaction mixture was cooled to -78 ꢀC,

(64) Rozhiewicz, D. I.; Janczewski, D.; Verboom, W.; Ravoo, B. J.;

Reinhoudt, D. N. Angew. Chem., Int. Ed. 2006, 45, 5292–5296.

(65) Sulfonamide 18 was reported previously with no characterization

data. See: (a) Luo, F.-T.; Wang, R.-T. Tetrahedron Lett. 1992, 33, 6835–

6838. (b) Ochifuji, N.; Mori, M. Tetrahedron Lett. 1995, 36, 9501–9504.

J. Org. Chem. Vol. 75, No. 22, 2010 7529

Altman et al.

JOCFeatured Article

1.58-1.29 (m, 8H), 0.96 (d, J = 7.5 Hz, 3H), 0.86-0.83 (m, 1H)

ppm; ¹³C NMR (125 MHz, CDCl₃) δ 143.1, 137.3, 135.5, 129.6,

127.1, 118.7, 49.1, 43.1, 37.7, 37.1, 35.8, 34.1, 33.0, 29.7, 29.1,

28.9, 26.6, 24.6, 21.5, 19.9 ppm; IR (thin film) 2907, 1599, 1458,

1324, 1159, 1095 cm^-1; HRMS (ESI) m/z 391.2417 (391.2419

calcd for C₂₂H₃₅N₂O₂S [MH]^þ).

Tricyclic Sulfonamide 28. p-Nitrophenylsulfonyl chloride

(96 mg, 0.43 mmol) was added to a stirred solution of amine

24 (175 mg, 0.434 mmol) and NEt₃(90 μL, 0.65 mmol) in

CH₂Cl₂(20 mL), and the yellow solution was stirred overnight

at rt. The reaction was quenched with 2 M HCl (10 mL), the

layers were separated, and the aqueous layer was extracted with

CH₂Cl₂(2 ꢀ 10 mL). The combined organic layers were washed

with brine (20 mL), dried with MgSO₄, and concentrated. The

resulting residue was purified by chromatography (hexanes/

EtOAc, 1:1) to give sulfonamide 28 as yellow foam/oil (216

mg, 88%): ¹H NMR (500 MHz, CDCl₃) δ 8.00 (m, 1H),

7.77-7.67 (m, 5H), 7.32 (d, J =8.0 Hz, 2H), 5.22 (s, 1H), 4.62

(t, J = 6.0 Hz, 1H), 3.72 (d, J = 11.2 Hz, 1H), 3.57 (d, J = 2.9

Hz, 1H), 3.00-2.93 (m, 3H), 2.43 (s, 3H), 2.21-2.10 (m, 3H),

1.96 (m, 1H), 1.81 (m, 2H), 1.76-1.36 (m, 6H), 1.22-1.07 (m,

3H), 0.90 (dt, J = 14.3, 2.3 Hz, 1H), 0.28 (d, J = 6.1 Hz, 3H)

ppm; ¹³C NMR (125 MHz, CDCl₃) δ 147.7, 143.2, 136.9, 135.0,

133.4, 132.1, 130.9, 129.6, 128.4, 127.0, 124.9, 60.3, 58.0, 50.6,

42.9, 40.2, 38.5, 36.6, 34.8, 34.2, 31.9, 29.1, 23.9, 21.6, 21.4, 21.0,

14.1 ppm.

N-(4-(3,7-Dimethyl-5,6,7,8-tetrahydronaphthalen-2-yl)butyl)-

4-methylbenzenesulfonamide (29). Trifluoromethanesulfonic acid

(13 mg, 0.085 mmol) was added to a solution of 28 (50 mg, 0.085

mmol) in toluene (5.0 mL). The reaction mixture was heated to

reflux for 2 h and then cooled to rt and quenched with saturated

aqueous NaHCO₃(10 mL). The layers were separated, and the

organic layer was extracted with ethyl acetate (3ꢀ10 mL). The

combined organic layers were dried with MgSO₄, concentrated in

vacuo, and the resulting residue was purified by column chroma-

tography (hexanes/EtOAc 4:1) to give 29 in low yield: ¹H NMR

(500 MHz, CDCl₃) δ 7.74 (d, J = 8.3 Hz, 2H), 7.30 (d, J = 8.0 Hz,

2H), 6.84 (s, 1H), 6.74 (s, 1H), 4.26 (t, J = 6.1 Hz, 1H), 2.86 (q, J =

14.5, 7.9 Hz, 2H), 2.73-2.70 (m, 2H), 2.48-2.39 (m, 2H), 2.42 (s,

3H), 2.33-2.28 (m, 2H), 2.17 (s, 3H), 1.86-1.80 (m, 2H),

1.55-1.50 (m, 3H), 1.36-1.25 (m, 2H), 1.04 (d, J = 6.5 Hz, 3H)

ppm; ¹³C NMR (125 MHz, CDCl₃) δ 143.4, 137.1, 136.9, 134.3,

134.2, 132.8, 130.5, 129.7, 129.3, 127.1, 43.2, 37.7, 32.3, 31.6, 29.5,

29.4, 28.7, 27.3, 22.0, 21.5, 18.8 ppm; IR (thin film) 3282, 2932,

1455, 1326, 1158, 1094, 814 cm^-1; HRMS (ESI) m/z 408.1964

(408.1973 calcd for C₂₃H₃₁NO₂SNa [(MNa)^þ]).

Methyl Cyanomethyl(3-methyl-6-(4-(4-methylphenylsulfonamido)-

butyl)-1,2,3,4,4a,5,8,8a-octahydronaphthalen-1-yl)carbamate (37).

Methyl chloroformate (26 μL, 0.340 mmol) was added to a

mixture of 23 (73 mg, 0.017 mmol) and K₂CO₃(0.14 g, 1.0

mmol) in THF (3.0 mL), and the yellow mixture was stirred

overnight at rt. The reaction mixture was directly purified by

column chromatography (hexanes/EtOAc 4:1f3:2) to provide

carbamate 37 as yellow oil (43 mg, 52%): ¹H NMR (500 MHz,

CDCl₃) δ 7.24 (d, J = 8.2 Hz, 2H), 7.29 (d, J = 8.1 Hz, 2H), 5.24

(s, 1H), 4.35 (t, J = 6.1 Hz, 1H), 4.26 (br s, 1H), 3.92 (d, J = 17.7

Hz, 1H), 3.79 (s, 3H), 2.92 (q, J = 13.3, 6.6 Hz, 2H), 2.43 (s, 3H),

2.26-2.08 (m, 4H), 1.97 (ddd, J = 12.9, 12.9, 5.5 Hz, 1H), 1.85

(t, J = 7.1 Hz, 2H), 1.71 (d, J = 15.7 Hz, 1H), 1.52-1.45 (m,

5H), 1.36 (m, 2H), 1.28 (m, 2H), 1.07 (dd, J = 7.3 Hz, 3H), 0.98

(m, 1H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 143.42, 136.9,

135.2, 129.7, 127.1, 117.7, 116.9, 53.8, 53.4, 43.1 36.9, 34.0, 32.4,

31.4, 29.3, 29.1, 28.4, 27.8, 24.4, 21.5, 20.3, 18.9, 14.6 ppm.⁶⁶

N-(4-((4a,8a)-5-(Cyanomethylamino)-7-methyl-1,4,4a,5,6,7,8,8a-

octahydronaphthalen-2-yl)butyl)-4-methylbenzenesulfonamide

(23). A mixture of amine 22 (484 mg, 1.2 mmol), chloroaceto-

nitrile (0.16 mL, 2.5 mmol), NEt₃(0.52 mL, 3.7 mmol), and

tetrabutylammonium iodide (114 mg, 0.31 mmol) was stirred in

THF (50 mL) at 70 ꢀC for 30 h. The reaction was cooled to rt

and concentrated in vacuo. The residue was redissolved in CH₂-

Cl₂(40 mL), washed with saturated aqueous NaHCO₃(30 mL).

The organic layer was dried with MgSO₄and concentrated. The

residue was purified by column chromatography (hexanes/

EtOAc 4:1f3:2) to give cyanomethylamine 23 as a tan oil

1

(418 mg, 78%): H NMR (500 MHz, CDCl₃) δ 7.76 (d, J =

8.0 Hz, 2H), 7.32 (d, J = 8.0 Hz, 2H), 5.29 (s, 1H), 4.63 (br s,

1H), 3.62-3.61 (m, 2H), 3.07-3.05 (m, 1H), 2.93 (q, J = 6.5 Hz,

2H), 2.44 (s, 3H), 2.03-2.00 (m, 2H), 1.96-1.93 (m, 3H), 1.88 (t,

J = 7.5 Hz, 2H), 1.77 (br s, 1H), 1.65-1.52 (m, 3H), 1.46-1.41

(m, 2H), 1.37-1.32 (m, 3H), 1.25-1.24 (m, 1H), 1.12-1.05 (m,

1H), 0.94 (d, J = 6.5 Hz, 3H) ppm; ¹³C NMR (125 MHz,

CDCl₃) δ 143.3, 137.1, 129.7, 127.2, 126.5, 119.1, 118.3, 60.5,

48.0, 43.2, 37.2, 37.1, 34.9, 33.8, 29.8, 29.2, 24.6, 21.6, 21.1, 20.5,

14.2, 12.6 ppm; IR (thin film) 3267, 2917, 1600, 1466, 1459, 1380,

1328, 1161, 1095 cm^-1; HRMS (ESI) m/z 452.2333 (452.2348

calcd for C₂₄H₃₅N₃O₂SNa^þ[MNa]^þ).

Tricyclic Amine 24. A solution of cyanomethyl amine 23 (420

mg, 0.97 mmol) in dry CHCl₃(90 mL) was added to AgO₂CCF₃

(709 mg, 3.21 mmol). The suspension was stirred at rt for 2 h,

after which time the reaction mixture was filtered with diato-

maceous earth. The filter cake was washed with CHCl₃(50 mL),

and the filtrate was washed with saturated aqueous NaHCO₃

(50 mL), dried with MgSO₄, and concentrated to give 24 as a tan

oil (350 mg, 90%): ¹H NMR (500 MHz, CDCl₃) δ 7.78 (d, J =

8.5 Hz, 2H), 7.33 (d, J = 8 Hz, 2H), 5.49 (s, 1H), 2.95 (t, J = 6.5

Hz, 3H), 2.80 (dd, J = 13.5, 2 Hz, 1H), 2.67 (d, J = 13.5 Hz, 1H),

2.46 (m, 4H), 2.46 (m, 1H), 2.10 (br s, 1H) 2.01 (br s, 1H),

1.88-1.86 (m, 2H), 1.81 (br s, 2H), 1.76-1.72 (m, 2H), 1.60-

1.54 (m, 1H), 1.53-1.50 (m, 1H), 1.49-1.44 (m, 3H), 1.40-1.36

(m, 1H), 1.24-1.19 (m, 1H), 1.19-1.12 (m, 1H), 0.90 (d, J = 6.0

Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 143.3, 138.2, 137.3,

130.6, 129.8, 127.2, 55.0, 47.9, 43.2, 40.6, 40.4, 36.5, 35.0, 33.2, 33.0,

32.4, 29.5, 24.9, 22.7, 22.0, 21.7 ppm; IR (thin film) 2928, 2873,

1600, 1466, 1457, 1326, 1305, 1160, 1095 cm^-1; HRMS (ESI) m/z

403.2412 (403.2419 calcd for C₂₃H₃₅N₂O₂S^þ[MH]^þ).

Tricyclic Carbamate 25. Triethylamine (0.10 mL, 0.75 mmol)

was added to a stirred solution of amine 24 (150 mg, 0.37 mmol)

and methylchloroformate (58 μL, 0.75 mmol) in CH₂Cl₂(4.2

mL), and the reaction was stirred at rt for 12 h. The reaction

mixture was concentrated, and the residue was purified by

chromatography (hexanes/EtOAc 4:1f3:2) to give carbamate

25 as a colorless oil (114 mg, 67%): ¹H NMR (500 MHz, CDCl₃)

δ 7.79 (d, J = 8.5 Hz, 2H), 7.33 (d, J = 8 Hz, 2H), 5.22 (s, 1H),

5.14 (t, J = 6 Hz, 1H), 3.89-3.86 (m, 1H), 3.63 (s, 3H), 3.55 (q,

J = 3 Hz, 1H), 3.03-3.00 (m, 1H), 2.94 (q, J = 6.5 Hz, 2H), 2.91

(dd, J = 12.5, 3.5 Hz, 1H), 2.45 (m, 4H), 2.10 (br s, 1H),

1.94-1.92 (m, 2H), 1.83-1.77 (m, 2H), 1.73-1.70 (m, 1H),

1.68-1.65 (m, 1H), 1.53-1.49 (m, 3H), 1.41-1.36 (m, 2H),

1.26-1.20 (m, 1H), 0.98-0.92 (m, 1H), 0.85 (d, J = 6.5 Hz, 3H)

ppm; ¹³C NMR (125 MHz, CDCl₃) δ 158.7, 143.3, 137.4, 137.2,

129.7, 128.9, 127.2, 55.9, 52.2, 49.6, 43.2, 41.0, 39.4, 36.9, 34.7,

33.7, 31.9, 31.8, 29.2, 24.7, 22.3, 22.0, 21.6 ppm; IR (thin film)

3269, 2945, 2917, 2850, 1702, 1685, 1442, 1326, 1307, 1294, 1268,

1243, 1230, 1201, 1157, 1094 cm^-1; HRMS (ESI) m/z 483.2290

(483.2293 calcd for C₂₅H₃₆N₂O₄SNa^þ[MNa]^þ).

Methyl

3-Methyl-6-(4-(4-methylphenylsulfonamido)butyl)-

1,2,3,4,4a,5,8,8a-octahydro-naphthalen-1-yl carbamate (38). Meth-

yl chloroformate (81 μL, 1.0 mmol) was added dropwise over

5 min to a stirred mixture of amine 22 (340 mg, 0.87 mmol) and

Na₂CO₃(120 mg, 1.1 mmol) in H₂O-CH₂Cl₂(1:1, 2 mL) at rt.

The reaction was stirred vigorously for 3 h, after which time the

layers were separated. The organic layer was dried with MgSO₄,

and the solvent was removed in vacuo. The resulting residue was

purified by column chromatography (hexanes/EtOAc 1:0f1:1)

(66) One ¹³C NMR signal was not observed.

7530 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

to provide carbamate 38 as a colorless solid (310 mg, 80%): ¹H

NMR (500 MHz, DMSO-d₆, 298.0 K, peak broadening caused

by dynamic NMR processes) δ 7.65 (d, J = 7.8 Hz, 2H), 7.45 (t,

J = 4.9 Hz, 1H), 7.37 (d, J = 7.8 Hz, 2H), 6.98 (br s, 1H), 5.21

(br s, 1H), 3.71 (br s, 1H), 3.49 (s, 3H), 2.69 (br s, 2H), 2.37 (s,

3H), 2.10 (d, J = 17.0 Hz, 1H), 2.05-1.86 (m, 4H), 1.85-1.57

(m, 4H), 1.48 (m, 1H), 1.40 (t, J = 9.6 Hz, 1H), 1.36-1.19 (m,

5H), 1.00 (d, J = 7.0 Hz, 3H), 0.93 (d, J = 12.7 Hz, 1H) ppm;

¹³C NMR (125 MHz, DMSO-d₆, 323.0 K, peak broadening

caused by dynamic NMR processes) δ 155.7, 144.2, 137.9, 134.5,

129.3, 126.3, 118.3, 50.8, 48.0, 42.3, 39.9, 36.4, 35.3, 33.6, 31.6,

28.3, 27.6, 26.3, 23.9, 20.7, 19.8, 19.0 ppm; IR (thin film) 3267,

2908, 1698, 1528, 1158 cm^-1; HRMS (ESI) m/z 471.2282

(471.2293 calcd for C₂₄H₃₆N₂O₄SNa [MNa]^þ).

Methyl (1H-Benzo[d][1,2,3]triazol-1-yl)methyl(3-methyl-6-(4-

(4-methylphenylsulfonamido)butyl)-1,2,3,4,4a,5,8,8a-octahydro-

naphthalen-1-yl)carbamate (39). Trifluoroacetic acid (4-5 drops)

was added to a solution of 38 (50 mg, 0.11 mmol) and (1H-

benzo[d][1,2,3]triazol-1-yl)methanol (0.050 mL, 0.33 mmol)

in dry acetonitrile (2.5 mL). The resulting solution was stirred

at rt overnight, and the solvent was removed in vacuo. The

residue was dissolved in Et₂O, and unreacted benzotriazole

was removed by filtration. The remaining material was puri-

fied by column chromatography (hexanes/EtOAc 4:1f1:1)

to afford benzotriazole 39 (45 mg, 70%). An analytical sample

was further purified using preparatory HPLC (hexanes/

EtOAc 19:1f3:2): ¹H NMR (500 MHz, CDCl₃) δ 8.05 (d,

J = 8.3 Hz, 1H), 8.01 (d, J = 8.2 Hz, 1H), 7.57-7.54 (m, 3H),

7.42 (t, J = 7.6 Hz, 1H), 7.20 (d, J = 8.0 Hz, 2H), 6.12 (s, 2H), 5.23

(s, 1H), 4.70 (br s, 1H), 3.88 (br s, 1H), 3.63 (s, 3H), 3.25 (t, J = 7.5

Hz, 2H), 2.39 (s, 3H), 2.05-1.93 (m, 6H), 1.78 (t, J = 7.2 Hz, 2H),

1.71-1.26 (m, 8H), 1.15 (m, 1H), 1.03 (d, J = 7.0 Hz, 3H) ppm;

¹³C NMR (125 MHz, CDCl₃) δ 156.7, 146.3, 144.2, 136.5, 135.7,

132.8, 130.0, 128.4, 127.1, 124.7, 120.0, 119.4, 111.0, 66.1, 59.3,

52.0, 50.0, 47.7, 37.2, 36.8, 35.2, 33.6, 29.9, 28.9, 27.5, 24.6, 21.7,

20.3, 15.5 ppm; IR (thin film) 3386, 3332, 1712, 1520, 1454, 1342,

1261, 1234, 1157, 1115, 1034, 933, 748 cm^-1; HRMS (ESI) m/z

602.2777 (602.2776 calcd for C₃₁H₄₁N₅O₄SNa [MNa]^þ).

Sulfonamide-Terminated Aza-Prins Cyclization To Form Tetra-

cyclic Sulfonamide 27. A stock solution of paraformaldehyde

(20 mg), TFA (1 mL), and CHCl₃(10 mL) was prepared in a

flame-dried round-bottom flask under nitrogen. An aliquot of

the stock formaldehyde solution (0.30 mL, ∼1 equiv of para-

formaldehyde and 20 equiv of TFA) was added to a solution

of amide 38 (0.10 g, 0.022 mmol) in CHCl₃(1 mL), and the

resulting mixture was stirred at rt until complete consumption of

the starting material was observed by electrospray MS analysis

(∼3 h). The reaction was quenched with saturated aqueous

NaHCO₃(3 mL) and extracted with CHCl₃(3 ꢀ 3 mL). The

combined organic layers were dried with MgSO₄and concen-

trated in vacuo. The crude residue was purified by preparative

HPLC (Alltima silica 5 μm, length 250 mm, ID 22 mm; hexanes/

EtOAc 7:3; 16 mL/min; retention time 9.8-11 min) to give

tetracyclic product 27 (20 mg, 20%) as a colorless solid: ¹H

NMR (500 MHz, CDCl₃) δ 7.66 (d, J = 8.2 Hz, 2H), 7.31 (d,

J = 8.0 Hz, 2H), 3.72 (m, 1H), 3.62 (s, 3H), 3.48 (ddd,

J = 14.6, 4.0, 4.0 Hz, 1H), 3.32 (t, J = 12.7 Hz, 1H), 2.74 (m,

1H), 2.50 (dd, J = 13.2, 5.0 Hz, 1H), 2.42 (s, 3H), 2.40-2.39 (m,

1H), 2.18-2.12 (m, 2H), 1.95-1.91 (m, 3H), 1.82 (ddd, J = 13.5,

10.8, 2.7 Hz, 1H), 1.85-1.73 (m, 2H), 1.63-1.45 (m, 4H), 1.01

(ddd, J = 12.8, 12.8, 3.0 Hz, 1H), 0.97 (ddd, J = 13.9, 3.5, 3.5

Hz, 1H), 0.88 (dd, J = 6.5 Hz, 3H), 0.83 (ddd, J = 14.4, 14.4, 3.0

Hz, 1H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 156.2, 143.3,

135.2, 129.8, 127.4, 59.4, 56.7, 54.3, 51.9, 49.3, 40.1, 38.9, 36.1,

36.0, 35.1, 34.1, 32.1, 30.9, 29.3, 24.9, 22.0, 21.7, 21.4 ppm; IR

(thin film) 1713 cm^-1; HRMS (ESI) m/z 483.2284 (483.2293

calcd for C₂₅H₃₆N₂O₄SNa [MNa]^þ).

Tetracyclic Carbamate 43. A flame-dried three-neck flask was

equipped with a stir bar, two rubber septa, and a coldfinger

condenser under nitrogen. The condenser and the round-

bottom flask were cooled to -78 ꢀC, and ammonia gas was

condensed into the three-neck round-bottom flask (∼10 mL).

To this solution at -78 ꢀC was added Na⁰(0.010 g, 0.46 mmol,

washed with HPLC grade pentane three times). The resulting

deep blue reaction mixture was stirred at -78 ꢀC for 5 min, and

then a solution of tetracyclic aza-Prins product 27 (7.0 mg, 0.015

mmol) in THF (3 mL) was added dropwise. The reaction was

stirred at -78 ꢀC for 15 min and quenched by the slow addition

of methanol (MeOH added dropwise until reaction becomes

clear, ∼2 mL) followed by the addition of saturated aqueous

NH₄Cl (3 mL). The resulting mixture was allowed to warm to rt

overnight open to the atmosphere. The aqueous solution was

extracted with CH₂Cl₂(3 ꢀ 10 mL), and the combined organic

solutions were dried with MgSO₄and concentrated in vacuo to

provide an orange oil. This residue was purified by column

chromatography (MeOH/CHCl₃/NH₄OH 10:90:1) to afford

carbamate 43 (5.0 mg, 98%) as a colorless oil. NMR spectra

are reported as the free base generated by the addition of

NaOCD₃to the NMR sample: ¹H NMR (500 MHz, CD₃OD)

δ 3.74 (br s, 1H), 3.60 (s, 3H), 2.88 (m, 1H), 2.76-2.66 (m, 2H),

2.57 (dd, J = 11.0, 3.6 Hz, 1H), 2.33 (m, 1H), 2.12 (d, J = 14.0

Hz, 1H), 1.99 (dd, J = 11.6, 2.8 Hz, 1H), 1.92 (ddd, J = 13.8,

11.1, 3.2 Hz, 1H), 1.88-1.71 (m, 3H), 1.70-1.50 (m, 4H),

1.48-1.42 (m, 2H), 1.40-1.29 (m, 2H), 1.06 (ddd, J = 12.8,

12.8, 3.1 Hz, 1H), 0.96 (ddd, J = 16.6, 4.6, 4.6 Hz, 1H), 0.87 (d,

J = 6.5 Hz, 3H), 0.86 (m, 1H) ppm; ¹³C NMR (125 MHz,

CD₃OD) δ 158.1, 60.9, 57.8, 56.6, 52.5, 41.5, 40.0, 38.4, 37.8,

37.1, 35.5, 34.1, 32.2, 31.3, 24.8, 22.6, 22.5 ppm;⁶⁶IR (thin film)

3363, 1706 cm^-1; HRMS (ESI) m/z 307.2386 (307.2393 calcd for

C₁₈H₃₁N₂O₂[MH]^þ).

5-epi-Nankakurine A (1). An Et₂O solution of LiAlH₄(0.30

mL, 0.29 mmol, 1.0 M) was added dropwise to a solution of N-

methyl carbamate 43 (9.0 mg, 0.029 mmol) in THF (3.0 mL) at

0 ꢀC. The reaction mixture was allowed to warm to rt, stirred

overnight at rt, quenched with H₂O (2.0 mL) and Rochelle salt

(20 mL), and stirred for an additional 2 h. The mixture was

transferred to a separatory funnel, diluted with Et₂O (20 mL),

agitated, and the two solutions were separated. The aqueous

solution was extracted with CH₂Cl₂(5 ꢀ 20 mL), and the

combined organic solutions were dried over MgSO₄, filtered,

and then concentrated in vacuo to yield orange oil residue. The

residue was purified by column chromatography (MeOH/

CHCl₃/NH₄OH 10:90:1) to afford diamine (()-1 (5.0 mg,

65%) as a yellow oil: IR (thin film) 3458, 1679 cm^-1; HRMS

(ESI) m/z 263.2490 (263.2487 calcd for C₁₇H₃₁N₂^þ[MH]^þ).

A portion of this sample was dissolved in 0.60 mL of CD₃OD

for NMR analysis, and 150 μL of NaOCD₃(∼0.1 M in CD₃OD)

was added to ensure that only the free base was present. Aliquots

of a solution of TFA in CD₃OD (15-25 μL portions of a 0.15 M

solution) were added to this sample, and ¹H NMR spectra were

obtained after each addition (Figure S1 in the Supporting Infor-

mation). Under no conditions were spectra obtained that matched

the ¹H NMR data reported for nankakurine A:^{2 1}H NMR (500

MHz, CD₃OD/CD₃ONa) δ 2.80 (m, 1H), 2.73 (dd, J = 14.6, 3.6

Hz, 1H), 2.54 (dd, J = 14.5, 10.9 Hz, 1H), 2.36 (br s, 1H), 2.28 (s,

3H), 2.28 (m, 1H), 2.02 (m, 1H), 1.95-1.82 (m, 3H), 1.75-1.66

(m, 4H), 1.54-1.43 (m, 4H), 1.19 (t, J = 2.9 Hz, 1H), 1.06 (m,

1H), 1.00 (ddd, J = 12.8, 12.8, 3.2 Hz, 1H), 0.86 (m, 1H), 0.86

(dd, J = 6.7 Hz, 3H), 0.74 (t, J = 12.8 Hz, 1H) ppm; ¹³C NMR

(125 MHz, CD₃OD) δ 63.3, 56.5, 56.1, 42.0, 40.7, 39.0, 37.8,

35.4, 34.4, 32.5, 32.2, 30.9, 23.0, 22.9, 22.6 ppm.⁶⁷

((Hex-5-ynyloxy)methyl)benzene (S3).⁴⁵A slurry of KH (35 g,

260 mmol) in THF (100 mL) was added to a mixture of alcohol

(67) Two ¹³C NMR signals were not observed.

J. Org. Chem. Vol. 75, No. 22, 2010 7531

Altman et al.

JOCFeatured Article

16 (28 mL, 250 mmol), tetra-n-butylammonium iodide (470 mg,

1.3 mmol), and benzyl bromide (33 mL, 280 mmol) in THF (500

mL) at 0 ꢀC. The suspension was warmed to rt and stirred

overnight. The reaction was quenched by the addition of H₂O

(400 mL), and the layers were separated. The aqueous layer

was extracted with Et₂O (2ꢀ200 mL). The combined organic

extracts were dried with MgSO₄and concentrated in vacuo.

The residue was purified by column chromatography (hexanes/

EtOAc 99:1) to give benzyl ether S3 as a yellow oil (46.5 g, 97%):

¹H NMR (500 MHz, CDCl₃) δ 7.43-7.33 (m, 4H), 7.31 (m, 1H),

4.53 (s, 2H), 3.52 (t, J = 6.3 Hz, 2H), 2.24 (ddd, J = 7.0, 7.0, 2.5

Hz, 2H), 1.97 (t, J = 2.5 Hz, 1H), 1.84-1.72 (m, 2H), 1.71-1.60

(m, 2H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 138.7, 128.5,

127.7, 127.6, 84.5, 73.0, 69.8, 68.6, 28.9, 25.4, 18.4 ppm; IR (thin

film) 3298, 2941, 2860, 1455, 1362, 1206, 1106 cm^-1; HRMS

(ESI) m/z 211.1100 (211.1099 calcd for C₁₃H₁₆ONa^þ[MNa]^þ).

((5-Methylenehept-6-enyloxy)methyl)benzene (48). Benzylidene-

[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro-

(tricyclohexylphosphine)ruthenium²²(1.12 g, 1.33 mmol) was

added to a solution of alkyne S3 (5.0 g, 27 mmol) and CH₂Cl₂

(400 mL), which was degassed with nitrogen for 60 min. The

solution was charged to a high-pressure bomb. The reaction bomb

was filled with ethylene gas (300 psi), vented, and repressurized

with ethylene (300 psi). This process was repeated a total of three

times. The reaction was stirred under pressure (300 psi) for 4-5 h.

After venting unreacted ethylene, the reaction mixture was trans-

ferred to a round-bottom flask containing silica gel, and the solvent

was removed in vacuo. The residue was dry loaded and purified by

column chromatography (hexanes/EtOAc, 19:1) to give diene 48

(5.2 g, 90%) as a tan oil: ¹H NMR (500 MHz, CDCl₃) δ 7.39 (d,

J = 4.5 Hz, 4H), 7.35-7.28 (m, 1H), 6.42 (dd, J = 17.6, 10.8 Hz,

1H), 5.27 (d, J = 17.6 Hz, 1H), 5.10 (d, J = 10.9 Hz, 1H), 5.05 (d,

J = 11.5 Hz, 2H), 4.55 (s, 2H), 3.54 (t, J= 6.4 Hz, 2H), 2.27 (t, J =

7.6 Hz, 2H), 1.80-1.68 (m, 2H), 1.67-1.59 (m, 2H) ppm; ¹³C

NMR (125 MHz, CDCl₃) δ 146.3, 139.1, 138.8, 128.5, 127.8, 127.6,

115.9, 113.3, 73.1, 70.4, 31.3, 29.8, 24.9 ppm; IR (thin film) 2939,

2858, 1596, 1455, 1362, 1104, 895 cm^-1; HRMS (ESI) m/z

217.1600 (217.1592 calcd for C₁₅H₂₀O^þ[MH]^þ).

vacuo, and the residue was purified by column chromatography

(hexanes/Et₂O, 19:1) to provide the ketone 50 (1.75 g, 99%) as a

colorless oil: [R]²³_Dþ 55 (c = 2.5, CHCl₃); ¹H NMR (500 MHz,

CDCl₃) δ 7.31 (d, J = 4.4 Hz, 4H), 7.28-7.19 (m, 1H), 5.31 (s,

1H), 4.47 (s, 2H), 3.43 (t, J = 6.5 Hz, 2H), 2.64 (t, J = 5.8 Hz,

1H), 2.54 (dd, J = 17.5, 2.9 Hz, 1H), 2.46-2.38 (m, 1H), 2.35

(dd, J = 13.1, 4.3 Hz, 1H), 2.24-2.10 (m, 1H), 1.96 (t, J = 12.6

Hz, 2H), 1.89 (td, J = 13.2, 6.4 Hz, 2H), 1.88-1.78 (m, 3H), 1.63

(ddd, J = 16, 11.9, 4.3 Hz, 1H), 1.54 (dd, J = 14.1, 6.9 Hz, 2H),

1.48-1.36 (m, 2H), 1.00 (d, J = 6.4 Hz, 3H) ppm; ¹³C NMR

(125 MHz, CDCl₃) δ 211.6, 138.9, 135.6, 128.5, 127.7, 127.6,

118.6, 72.9, 70.4, 49.7, 47.2, 38.7, 37.6, 35.7, 30.8, 30.1, 29.5,

24.2, 23.8, 22.6 ppm; IR (thin film) 3397, 2913, 2868, 1708, 1454,

1104 cm^-1; HRMS (ESI) m/z 349.2143 (349.2144 calcd for

C₂₂H₃₀O₂Na^þ[MNa]^þ).

Methyl N⁰-6-(4-(Benzyloxy)butyl)-3-methyl-1,2,3,4,4a,5,8,8a-

octahydronaphthalen-1-ylmethanehydrazonoperoxoate (51). A

solution of methyl hydrazidocarbamate (0.010 g, 0.11 mmol)

and decalone 50 (33 g, 0.010 mmol) was stirred at rt for 3 days

in MeOH (1.0 mL), and NaCNBH₃(6.9 mg, 0.11 mmol) and

bromocresol green indicator (∼1 mg) were added to the

solution. A MeOH/HCl solution then was added dropwise

over 30 min at a rate to maintain the pH ∼3-5. (A green/blue

color was maintained for 30 min, and the reaction was

complete when a yellow color persisted.) The reaction mixture

was quenched with 6 N KOH (1.0 mL) and stirred for 1 h. This

mixture was diluted with saturated aqueous NH₄Cl (5 mL)

and extracted with CH₂Cl₂(5 ꢀ mL). The combined organic

layers were dried with MgSO₄and concentrated in vacuo. The

residue was purified by column chromatography (hexanes/

EtOAc 4:1) to give hydrazide 51 (4.8 mg, 12%) as a colorless

solid: ¹H NMR (500 MHz, CDCl₃) δ 7.36-7.26 (m, 5H), 6.04

(br s, 1H), 5.41 (s, 1H), 4.51 (s, 2H), 3.71 (s, 3H), 3.48 (t, J = 6.2

Hz, 2H), 3.15 (br s, 1H), 2.18-1.84 (m, 8H), 1.67-1.41 (m,

9H), 1.16 (m, 1H), 0.95 (d, J = 6.6 Hz, 3H) ppm; ¹³C NMR

(125 MHz, CDCl₃) δ 158.1, 138.9, 128.6, 127.8, 127.7, 126.7,

119.1, 73.1, 70.6, 52.5, 37.81, 34.6, 33.9, 32.2, 30.4, 29.9, 29.6,

24.4, 22.9, 20.7, 14.4 ppm;⁶⁷IR (thin film) 3324, 1726, 1455,,

1365, 1261, 1101 cm^-1; HRMS (ESI) m/z 423.2618 (423.2624

calcd for C₂₄H₃₆N₂O₃Na^þ[MNa]^þ).

N⁰-(6-(4-(Benzyloxy)butyl)-3-methyl-1,2,3,4,4a,5,8,8a-octa-

hydronaphthalen-1-yl)-4-methylbenzenesulfonohydrazide (52). A

solution of tosylhydrazide (0.24 g, 1.3 mmol) in MeOH (15 mL)

was added over 30 h by syringe pump to a solution of 50 (0.400 g,

1.23 mmol) and KOH (1.65 g, 29.5 mmol) in MeOH (15 mL) at

rt. The reaction was quenched with saturated aqueous NH₄Cl

(30 mL) and extracted with CH₂Cl₂(3 ꢀ 20 mL). The combined

organic extracts were dried with MgSO₄and concentrated. The

residue was purified by column chromatography (hexanes/

EtOAc 9:1f3:1) to provide the corresponding hydrazone

(0.070 g) as a colorless solid. A mixture of MeOH and concen-

trated HCl (9:1) was added dropwise at rt over 1 h to a stirred

mixture of hydrazone (0.70 g, 0.14 mmol), NaBH₃CN (0.010 g,

0.15 mmol), and a trace (∼ 0.2 mg) of methyl orange in MeOH

(3 mL). The rate of addition was controlled so that the color

of the reaction mixture remained orange-red (pH = 3-4) over

1 h. The reaction was quenched with aqueous 6 N KOH

(10 mL). The aqueous layer was extracted with Et₂O (5ꢀ10 mL).

The combined organic layers were washed with water (30 mL)

and brine (30 mL), dried with MgSO₄, and concentrated in

vacuo. Purification by column chromatography (hexanes/EtOAc

9:1f3:1) provided 52 as a colorless solid (45 mg, 7%, 2 steps):

¹H NMR (500 MHz, CDCl₃) δ 7.83-7.78 (m, 3H), 7.36-7.32

(m, 4H), 7.30-7.28 (m, 3H), 5.78 (s, 1H), 5.23 (s, 1H), 4.51 (s,

2H), 3.49-3.44 (m, 2H), 3.32 (m, 1H), 2.44 (s, 3H), 2.01-1.73

(m, 6H), 1.60-1.38 (m, 8H), 1.03-0.86 (m, 5H), 0.82 (d, J = 6.8

Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 144.1, 138.9,

135.7, 129.8, 128.6, 128.4, 127.9, 127.8, 127.7, 118.6, 73.1, 70.6,

(3⁰R,4a⁰S,8a⁰R)-6⁰-(4-(Benzyloxy)butyl)-3⁰-methyl-3⁰,4⁰,4a⁰,5⁰,-

8⁰,8a⁰-hexahydro-2⁰H-spiro[[1,3]dioxolane-2,1⁰-naphthalene] (S4).

Trimethylsilyl trifluoromethanesulfonate (0.20 mL, 1.1 mmol)

was added dropwise to a solution of enone (þ)-9⁴⁶(1.31 g, 11.9

mmol, >99% ee as determined by chiral HPLC) in CH₂Cl₂(0.75

mL) at -78 ꢀC. 1,2-Bis(trimethylsiloxy)ethane (2.93 mL, 11.9

mmol) was added, and the resulting solution was stirred at -78

ꢀC for 5 min. Diene 48 (2.35 g, 10.9 mmol) was added, and the

reaction was stirred at -78 ꢀC for 22 h. The reaction was then

quenched with NEt₃(0.25 mL), and the reaction was warmed to

rt. The solution was passed through a small plug of neutral

alumina and eluted with 50 mL of CH₂Cl₂, and the eluent was

concentrated in vacuo. The residue was purified by column

chromatography (hexanes/Et₂O 49:1) to give ketal S4 (2.53 g,

1

64%) as a clear oil: [R]²³-1.7 (c = 1.25, CH₃Cl); H NMR

D

(500 MHz, CDCl₃) δ 7.35 (d, J = 4.4 Hz, 4H), 7.29 (m, 1H), 5.27

(s, 1H), 4.52 (s, 2H), 3.95-3.82 (m, 4H), 3.48 (t, J = 6.6 Hz, 2H),

2.18-2.02 (m, 4H), 1.97 (t, J = 7.3 Hz, 2H), 1.97 (m, 1H),

1.93-1.86 (m, 1H), 1.80 (dd, J = 13.7, 3.9 Hz, 2H), 1.66-1.55

(m, 3H), 1.53-1.40 (m, 2H), 1.22-1.12 (m, 2H), 0.98 (d, J = 6.9

Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 138.9, 136.7,

128.5, 127.7, 127.5, 118.8, 111.7, 73.0, 70.6, 65.2, 64.4, 41.6, 39.7,

37.8, 37.2, 32.0, 31.1, 29.3, 26.2, 24.2, 24.2, 21.8 ppm; IR (thin

film) 2916, 2871, 1455, 1102, 1048, 949 cm^-1; HRMS (ESI) m/z

388.2852 (388.2852 calcd for C₂₄H₃₄O₃NH₄^þ[MNH₄]^þ).

(3R,4aS,8aR)-6-(4-(Benzyloxy)butyl)-3-methyl-3,4,4a,5,8,8a-

hexahydronaphthalen-1(2H)-one (50). A preformed mixture of

FeCl₃/SiO₂²⁶(0.375 g) was added to a solution of ketal S4 (2.0 g,

5.4 mmol) in acetone (50 mL, ACS grade), and the resulting

suspension was stirred at rt for 2 h. The solvent was removed in

7532 J. Org. Chem. Vol. 75, No. 22, 2010

Altman et al.

JOCFeatured Article

41.7, 37.8, 37.6, 37.5, 34.4, 33.5, 30.4, 29.9, 29.6, 29.5, 25.5, 24.4,

21.8 ppm; IR (thin film) 1454, 1362, 1207, 1103, 1034, 1011,

and then quenched with 37% aqueous formaldehyde (2 mL).

Bromocresol green indicator (∼1 mg) and NaCNBH₃(50 mg,

0.78 mmol) were added, and a solution of MeOH/HCl was then

added dropwise over 30 min at a rate to maintain a pH ∼3-5. (A

green/blue color was maintained for 30 min, and the reaction

was complete when a yellow color persisted.) The reaction

mixture was then quenched with aqueous 6 N KOH (2 mL)

and stirred for 1 h. The mixture was diluted with saturated

aqueous NH₄Cl and extracted with CH₂Cl₂(5 ꢀ 10 mL). The

combined organic layers were dried with MgSO₄and concen-

trated in vacuo. The residue was purified by column chroma-

tography (hexanes/acetone 7:3) to give tricyclic amino amide 59

(100 mg, 80%) as a yellow oil: [R]²⁴_Dþ10 (c = 0.8, CHCl₃); ¹H

NMR (500 MHz, CDCl₃) δ 7.71 (d, J = 7.4 Hz, 2H), 7.47 (t, J =

7.2 Hz, 1H), 7.40 (t, J = 7.5 Hz, 2H), 7.36-7.19 (m, 5H), 5.74 (s,

1H), 4.44 (s, 2H), 3.43 (dddd, J = 21.8, 9.0, 6.5, 6.5 Hz, 2H), 2.93

(d, J = 11.8, 1H), 2.60 (br s, 1H), 2.42 (t, J = 12.2, 1H), 2.26

(ddd, J = 13.0, 13.0, 4.2 Hz, 1H), 2.14 (dd, J = 11.8, 2.5 Hz,

1H), 2.03 (s, 3H), 1.97-1.87 (m, 4H), 1.81-1.79 (m, 2H), 1.71

(dd, J = 11.8, 5.7 Hz, 1H), 1.59 (ddd, J = 14.5, 14.5, 6.8 Hz,

2H), 1.52-1.37 (m, 4H), 1.29-1.24 (m, 1H), 1.18 (ddd, J = 12.4,

814 cm^-1

.

N⁰-((1S,3R,4aS,8aR)-6-(4-(Benzyloxy)butyl)-3-methyl-1,2,3,4,-

4a,5,8,8a-octahydronaphthalen-1-yl)benzohydrazide (53). A so-

lution of benzoic hydrazide (0.38 g, 2.8 mmol) and 50 (0.90 g,

2.8 mmol) was stirred at rt for 3 days in MeOH (20 mL), and

NaCNBH₃(0.190 g, 3.03 mmol) and bromocresol green indi-

cator (∼1 mg) were added to the solution. A MeOH/HCl

solution then was added dropwise over 30 min at a rate to

maintain a pH ∼3-5. (A green/blue color was maintained for 30

min, and the reaction was complete when a yellow color

persisted.) The reaction mixture was quenched with 6 N KOH

(2 mL) and stirred for 1 h. This mixture was diluted with satu-

rated aqueous NH₄Cl and extracted with CH₂Cl₂(5 ꢀ 20 mL).

The combined organic layers were dried with MgSO₄and

concentrated in vacuo. The residue was purified by column

chromatography (hexanes/EtOAc 4:1) to give 53 (0.98 g, 80%)

as a colorless solid: mp 98-101 ꢀC; [R]²⁴_D-21 (c = 1.1, CHCl₃);

¹H NMR (500 MHz, DMSO-d₆, 323 K, peak broadening caused

by dynamic NMR processes) δ 9.90 (br s, 1H), 7.81 (d, J = 6.5

Hz, 2H), 7.51 (t, J = 7.3 Hz, 1H), 7.44 (t, J = 7.7 Hz, 2H),

7.33-7.24 (m, 5H), 5.35 (br s, 1H), 4.88 (br s, 1H), 4.42 (s, 3H),

3.40 (t, J = 6.3 Hz, 2H), 3.11 (br s, 1H), 2.25-1.93 (m, 5H),

1.90-1.87 (m, 3H), 1.64 (m, 1H), 1.54-1.46 (m, 3H), 1.42-1.38

12.8, 4.9 Hz, 1H), 0.89 (m, 1H), 0.84 (d, J = 6.4, 3H) ppm; ¹³

C

NMR (125 MHz, CDCl₃) δ 166.8, 138.9, 136.1, 131.3, 128.7,

128.5, 127.8, 127.6, 126.9, 73.0, 70.6, 63.7, 60.4, 59.3, 43.4, 40.6,

39.0, 37.7, 36.2, 35.4, 34.2, 32.9, 31.1, 30.2, 22.8, 21.2, 20.8 ppm;

IR (thin film) 2921, 2852, 2771, 1644, 1528, 1488, 1455, 1102

cm^-1; HRMS (ESI) m/z 475.3329 (475.3325 calcd for C₃₁H₄₃-

N₂O₂^þ[MH]^þ).

(m, 2H), 1.24 (m, 1H), 1.03 (m, 1H), 0.97 (d, J = 7.0 Hz, 3H); ¹³

C

NMR (125 MHz, DMSO-d₆, 340 K) δ 149.5, 138.5, 130.6, 127.8,

127.7, 126.9, 126.8, 126.7, 118.6, 71.5, 69.3, 36.6, 34.1, 33.4, 28.5,

28.3, 23.5, 19.8 ppm; IR (thin film) 3291, 2915, 2862, 1630, 1457,

Diamino Alcohol (S5). A round-bottom flask containing

diamine 59 (140 mg, 0.29 mmol), Pearlman’s catalyst (20 wt %

Pd(OH)₂/C, 41 mg, 0.030 mmol), concentrated HCl (1 drop),

and MeOH (10 mL) was fitted with a septa and a balloon of

hydrogen gas. The reaction vessel was evacuated and backfilled

with hydrogen five times. The reaction mixture was stirred at rt

for 1 h and filtered through a syringe filter (25 mm, 0.45 μm pore

size), and the filtrate was concentrated in vacuo. The residue was

purified by column chromatography (MeOH/CHCl₃/NH₄OH

5:95:1) to give diamino alcohol S5 (110 mg, 97%) as a colorless

solid: mp 60-63 ꢀC; [R]²⁴_Dþ 14 (c = 1.15, CHCl₃); ¹H NMR

(500 MHz, CDCl₃) δ 7.73 (d, J = 7.3 Hz, 2H), 7.48 (t, J = 7.3

Hz, 1H), 7.42 (t, J = 7.8 Hz, 2H), 5.82 (s, 1H), 3.67-3.59 (m,

2H), 2.94 (d, J = 11.8 Hz, 1H), 2.57 (br s, 1H), 2.43 (t, J = 12.4

Hz, 1H), 2.33 (ddd, J = 12.8, 12.8, 4.2 Hz, 1H), 2.15 (dd, J =

11.8, 2.9 Hz, 1H), 2.05 (s, 3H), 1.99-1.82, (m, 7H), 1.72 (dd, J =

11.9, 5.8 Hz, 1H), 1.63-1.47 (m, 5H), 1.40 (m, 1H), 1.30 (m, 1H),

1.19 (ddd, J = 12.7, 12.4 4.9 Hz, 1H), 0.91 (m, 1H), 0.86 (d, J =

6.5 Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ 167.1, 135.9,

131.4, 128.8, 126.9, 63.7, 62.6, 60.5, 59.3, 43.4, 40.6, 39.0, 37.8,

36.4, 35.3, 33.8, 32.9, 32.8, 31.1, 22.8, 21.2, 20.0 ppm; IR (thin

1315, 1103 cm^{-1 68}

HRMS (ESI) m/z 469.2823 (469.2831 calcd

;

for C₂₉H₃₈N₂O₂Na^þ[MNa]^þ).

Intramolecular Azomethine Imine Cycloaddition To Form

Tetracyclic Pyrazolidine 54. Benzoyl hydrazide 53 (250 mg,

0.56 mmol) was added to a sealable tube containing para-

˚

formaldehyde (84 mg, 2.8 mmol), 4 A molecular sieves powder

(1.7 g, activated by flame drying under vacuum), diisopropyl-

ethylamine (93 μL, 0.56 mmol), and toluene (12 mL). The

resulting suspension was placed in an oil bath preheated to

115 ꢀC and stirred at 115 ꢀC until the starting material was

completely consumed (∼20 h) as monitored by electrospray MS

analysis or TLC (hexanes/EtOAc 4:1). The reaction mixture was

allowed to cool to rt, and the molecular sieves were removed by

filtration through a plug of neutral alumina, eluting with Et₂O

(50 mL). The solution was concentrated in vacuo, and the

residue was purified by column chromatography (hexanes/

EtOAc 4:1) to give the tetracyclic product 54 (218 mg, 85%)

as a colorless solid: mp 123-126 ꢀC; [R]²³-16 (c = 1.6,

D

1

CHCl₃); H NMR (500 MHz, CDCl₃) δ 7.52-7.50 (m, 2H),

7.38-7.25 (m, 8H), 4.47 (s, 2H), 3.47 (ddd, J = 21.7, 9.3, 6.2 Hz,

2H), 3.19 (m, 1H), 2.90 (t, J = 4.3 Hz, 1H), 2.73 (d, J = 10.8 Hz,

1H), 2.57 (ddd, J = 13.2, 13.2, 3.9 Hz, 1H), 2.40 (t, J = 4.8 Hz,

1H), 2.24 (d, J = 14.8 Hz, 1H), 2.07 (m, 1H), 1.89 (dd, J = 14.7,

11.1 Hz, 1H), 1.82-1.67 (m, 4H), 1.67-1.48 (m, 6H), 1.35-1.26

(m, 1H), 1.16 (ddd, J = 12.4, 1.9, 1.9 Hz, 1H), 1.04 (ddd, J =

12.9, 12.9, 4.9 Hz, 1H), 0.81 (ddd, J = 13.5, 13.3, 5.7 Hz, 1H)

0.73 (d, J = 6.3 Hz, 3H) ppm; ¹³C NMR (125 MHz, CDCl₃) δ

167.9, 138.9, 138.2, 129.7, 128.5, 128.1, 127.9, 127.6, 127.6, 73.0,

70.3, 69.9, 62.8, 62.4, 42.2, 40.2, 38.1, 36.3, 34.5, 34.2, 33.7, 33.4,

30.1, 23.5, 22.5, 21.1 ppm; IR (thin film) 1624 cm^-1; HRMS

(ESI) m/z 459.3009 (459.3011 calcd for C₃₀H₃₉N₂O₂^þ[MH]^þ).

Tricyclic Amino Amide (59). A solution of SmI₂(9 mL, ∼1 M

in THF)^51,59was added at a rapid rate to a stirring solution of

tetracyclic pyrazolidine 54 (120 mg, 0.26 mmol) in MeOH (1.0

mL), which had been sparged with argon for 30 min. The deep

blue reaction mixture was stirred at rt under argon for 30 min

film) 3343, 2944, 2921, 2865, 2771, 1644, 1530, 1457 cm^-1

;

þ

HRMS (ESI) m/z 385.2838 (385.2885 calcd for C₂₄H₃₇N₂O₂

[MH]^þ).

52

Diamino Alcohol (60). A THF solution of AlH₃(3.6 mL,

1.8 mmol, ∼0.5 M) was added to a solution of amide S5 (70 mg,

0.18 mmol) in THF (4 mL). The reaction mixture was stirred at

rt for 3 h and then quenched with Rochelle salt. The resulting

mixture was stirred overnight and then extracted with CH₂Cl₂

(10 ꢀ 10 mL). The combined organic extracts were dried over

MgSO₄, filtered, and concentrated in vacuo. Purification of the

residue by column chromatography (MeOH/CHCl₃/NH₄OH

0:99:1f10:90:1) afforded diamino alcohol 60 (50 mg, 74%) as a

colorless oil: [R]²³_Dþ 4.3 (c = 0.7, MeOH); ¹H NMR (500 MHz,

CDCl₃) δ 7.38 (d, J = 7.3 Hz, 2H), 7.31 (t, J = 7.3 Hz, 1H), 7.23

(t, J = 7.3 Hz, 1H), 3.67 (t, J = 6.6 Hz, 2H), 3.62 (d, J = 3.6 Hz,

1H), 3.60 (m, 1H), 3.07 (d, J = 11.6 Hz, 1H), 2.19 (t, J = 12.8

Hz, 1H), 2.13 (dd, J = 11.6, 2.9 Hz, 1H), 2.08 (s, 3H), 2.01-1.84

(m, 4H), 1.83-1.62 (m, 5H), 1.55-1.34 (m, 10H), 1.16 (ddd, J =

12.6, 12.4, 4.9 Hz, 1H), 0.87 (m, 1H), 0.83 (d, J = 6.5 Hz, 3H)

(68) Several ¹³C NMR signals were not observed because of peak broad-

ening caused by dynamic NMR processes.

J. Org. Chem. Vol. 75, No. 22, 2010 7533

Altman et al.

JOCFeatured Article

ppm; ¹³C NMR (125 MHz, CDCl₃) δ 141.9, 128.6, 128.5, 126.9,

63.8, 63.4, 58.6, 57.4, 45.4, 43.6, 41.0, 39.5, 39.2, 36.6, 36.1, 33.9,

33.8, 33.5, 32.0, 22.9, 21.1, 19.4 ppm; IR (thin film) 3342, 2921,

2865, 2769, 1455, 1061 cm^-1; HRMS (ESI) m/z 371.3062

(371.3062 calcd for C₂₄H₃₉N₂O₂^þ[MH]^þ).

N-Benzyl Nankakurine A (61). Methanesulfonyl chloride

(25 μL, 0.32 mmol) was added dropwise to a solution of

diamino alcohol 60 (110 mg, 0.29 mmol) and NEt₃(54 μL,

0.38 mmol) in CH₂Cl₂(5.0 mL) at -40 ꢀC. The reaction

was stirred at -40 ꢀC for 30 min, and then the reaction was

quenched at -40 ꢀC with MeOH (0.6 mL) and NEt₃(0.2 mL).

The resulting solution was allowed to warm to rt and stirred

for 3 h. The solvent was removed in vacuo, and the residue was

purified by column chromatography (MeOH/CHCl₃/NH₄OH

layers were dried over MgSO₄, filtered, and concentrated in

vacuo. The residue was purified by column chromatography

(MeOH/CHCl₃/NH₄OH 10:90:1) to give (þ)-nankakurine B

(20 mg, 80%) as a colorless solid: [R]²⁴_Dþ 12 (c = 1.5, MeOH);

IR (thin film) 3449, 1680 cm^-1; HRMS (ESI) m/z 276.2635

(276.2644 calcd for C₁₈H₃₃N₂^þ[MH]^þ).

A portion of this sample was dissolved in 0.60 mL of CD₃OD

and 150 μL of NaOCD₃(∼0.1 M in CD₃OD) was added. ¹H and

¹³C NMR spectra of the free base were obtained, and aliquots of

a solution of TFA in CD₃OD (15-25 μL portions of a 0.15 M

solution) were successively added to the sample Figure 3.

Spectra matching the reported spectrum of (þ)-nankakurine

B⁴were obtained after the addition of TFA•CD₃OD (Figures S4

1

and S5). NMR spectra of the free base: H NMR (500 MHz,

0:99:1f10:90:1) to afford diamine 61 (100 mg, 96%) as a

CD₃OD/CD₃ONa) δ 3.09 (ddd, J = 11.4, 5.1, 2.7 Hz, 1H), 3.0

(br s, 1H), 2.80 (br s, 1H), 2.49 (t, J = 12.6 Hz, 1H), 2.41 (s, 3H),

2.10 (s, 3H), 2.08 (dd, J = 11.9, 3.0 Hz, 1H), 2.05-1.93 (m, 3H),

1.92-1.77 (m, 4H), 1.76-1.54 (m, 5H), 1.53-1.38 (m, 4H), 1.22

(ddd, J = 12.7, 12.7, 4.6 Hz, 1H), 0.90 (m, 1H), 0.85 (d, J = 6.5

Hz, 3H) ppm; ¹³C NMR (125 MHz, CD₃OD) δ 64.9, 60.4, 58.6,

43.4, 42.2, 40.3, 36.9, 35.2, 34.5, 32.7, 25.9, 23.2, 22.3, 20.6, 19.1

ppm.⁶⁹

1

colorless oil: [R]²⁴þ 4.6 (c = 1.0, CHCl₃); H NMR (500

D

MHz, CD₃OD) δ 7.35 (d, J = 7.4 Hz, 2H), 7.24 (t, J = 7.4 Hz,

2H), 7.14 (t, J = 7.4 Hz, 1H), 3.88 (s, 2H), 3.35 (ddd, J = 10.9,

2.3, 2.3 Hz, 1H), 2.80 (m, 1H), 2.72 (t, J = 12.5 Hz, 1H), 2.49

(d, J = 13.8 Hz, 1H), 2.34 (br s, 1H), 2.14 (s, 3H), 2.10-1.93

(m, 5H), 1.85 (m, 1H), 1.75 (m, 1H), 1.65-1.33 (m, 19H), 1.14

(ddd, J = 12.7, 12.7, 4.9 Hz, 1H), 0.88 (m, 1H), 0.82 (d, J =

6.6 Hz, 3H) ppm; ¹³C NMR (125 MHz, CD₃OD) δ 144.6,

129.3, 129.0, 127.3, 64.9, 59.3, 59.1, 50.8, 44.8, 43.5, 42.5,

42.1, 40.5, 37.6, 34.8, 33.3, 32.9, 31.1, 23.2, 22.2, 21.4, 21.2

ppm; IR (thin film) 2944, 2921, 2863, 2769, 1621, 1453, 1104

cm^-1; HRMS (ESI) m/z 353.2953 (353.2957 calcd for

Neurite Growth Assay. H19-7 cells (ATCC) were derived from

hippocampi from E17 rat embryos and immortalized by retro-

viral transduction of SV40 large T antigen. The H19-7 cells were

plated at low density (20 000 cells/well) in 48-well cell culture

plates in N₂-supplemented DMEM. After 24 h in culture, cells

were treated with 0.3-10 μM concentrations of either nankak-

urine A (2) or nankakurine B (3) or with 1 μM of a reference

compound in culture medium. After treatment for 24 h, cells

were fixed with 4% paraformaldehyde for 20 min, permeabil-

ized with Triton X100, and incubated with an antibody against

neuronal class b-III tubulin (Tuj1, Covance) overnight at 4 ꢀC.

Cells were incubated with a secondary Alexa Fluor 546 goat

anti-mouse antibody for 30 min at room temperature. Both

length of neurites stained by Tuj1 and cell counting were quantified

using a fluorescence microscope (Zeiss) coupled to an automated

image analysis system (ExploraNova). The ratio between these two

end points (total length of neurites per cell in μm) allowed us to

evaluate the activity of nankakurines on neurite outgrowth of H19-

7 cells. Data are expressed as percent of neurite length in treated

cells compared to nontreated cells (control).

C

₂₄H₃₇N₂^þ[MH]^þ).

(þ)-Nankakurine A (2). A round-bottom flask containing N-

benzylnankakurine A (61) (90 mg, 0.26 mmol), palladium on

carbon catalyst (10 wt % Pd/C, 27 mg, 0.03 mmol), concentrated

HCl (1 drop), and MeOH (4.0 mL) was fitted with a septa and a

balloon of hydrogen gas. The reaction vessel was evacuated and

backfilled with hydrogen five times. The reaction mixture was

stirred at rt for 1 h and then filtered through a syringe filter (25

mm, 0.45 μm pore size), and the filtrate concentrated in vacuo.

The residue was purified by column chromatography (MeOH/

CHCl₃/NH₄OH 5:95:1) to give (þ)-nankakurine A (66 mg,

99%) as a colorless solid: [R]²⁴þ 13 (c = 0.4, MeOH); IR

D

(thin film) 3397, 1671 cm^-1; HRMS (ESI) m/z 263.2484

(263.2487 calcd for C₁₇H₃₁N₂^þ[MH]^þ).

A portion of this sample was dissolved in 0.60 mL of CD₃OD,

and 150 μL of NaOCD₃(∼0.1 M in CD₃OD) was added to

ensure that only the free base was present. Aliquots of a solution

of TFA in CD₃OD (15-25 μL portions of a 0.15 M solution)

Acknowledgment. This research was supported by the

NIH Neurological Disorders & Stroke Institute (NS-12389),

and by unrestricted grants from Amgen and Merck. J.R.A. and

R.A.A. were funded by the University of California President’s

Postdoctoral Fellowship and the NIH (5F32GM085989), re-

spectively. NMR and mass spectra were obtained at UC Irvine

using instrumentation acquired with the assistance of NSF and

NIH Shared Instrumentation grants. We are grateful to Dr.

Hiroshi Morita, Department of Pharmacognosy, Faculty of

Pharmaceutical Sciences, Hoshi University, Japan, for copies

1

were successively added to the sample, and H NMR spectra

were obtained after each addition (Figure 2). Spectra matching

the reported spectrum of (þ)-nankakurine A²were obtained

upon addition of several portions of TFA•CD₃OD (Figures S2

1

and S3). NMR spectra of the free base: H NMR (500 MHz,

CD₃OD/CD₃ONa) δ 3.00 (ddd, J = 11.9, 5.1, 2.7 Hz, 1H), 2.80

(t, J = 4.5 Hz, 2H), 2.28 (t, J = 12.7 Hz, 1H), 2.13 (dd, J = 12.7,

2.8 Hz, 1H), 2.11 (s, 3H), 2.05-2.02 (m, 2H), 2.01-1.90 (m, 1H),

1.89-1.76 (m, 3H), 1.69-1.67 (m, 3H), 1.66-1.44 (m, 7H), 1.20

(ddd, J = 12.7, 12.7, 5.1 Hz, 1H), 0.89 (m, 1H), 0.84 (d, J = 6.6

Hz, 3H) ppm; ¹³C NMR (125 MHz, CD₃OD) δ 65.2, 58.7, 56.0,

43.6, 42.0, 41.4, 40.1, 37.6, 34.8, 34.6, 32.7, 26.5, 23.2, 22.2,

21.1 ppm.^2,66

(þ)-Nankakurine B (3). To a solution of synthetic (þ)-nan-

kakurine A (24 mg, 0.9 mmol) in MeOH (3 mL) was added

NaCNBH₃(17 mg, 0.28 mmol). To the resulting solution was

added a MeOH/HCl solution dropwise over 30 min at a rate to

maintain a pH of ∼3-5 (no indicator was used because it was

difficult to separate from nankakurine B). The reaction mixture

was quenched with aqueous 6 N KOH and stirred for 1 h,

saturated aqueous NH₄Cl was added, and the mixture was

extracted with CH₂Cl₂(5 ꢀ 20 mL). The combined organic

1

of H and ¹³C NMR spectra of natural nankakurine B;

Dr. Dominique Lesuisse, Aging Department, Sanofi-Aventis

R&D, for arranging for neurotrophic testing of synthetic

nankakurines A and B; and Dr. Joe Ziller, X-ray Crystal-

lography Facility Director, UC Irvine, for X-ray analyses.

1

Supporting Information Available: Copies of H and ¹³C

NMR spectra of new compounds; ¹H NMR comparison of

synthetic 1, 2, and 3 with natural 2 and 3; CIF file for compound

54. This material is available free of charge via the Internet at

http://pubs.acs.org.

(69) Three ¹³C NMR signals were not observed.

7534 J. Org. Chem. Vol. 75, No. 22, 2010

Article Doi

Total synthesis of (+)-nankakurines A and B and (±)-5-epi- nankakurine A

DOI: 10.1021/jo101619d

Source and publish data:

Authors:

Article abstract of DOI:10.1021/jo101619d

Full text of DOI:10.1021/jo101619d

Products guided by the article

R&D Labs maybe for 1255772-52-1

Relevant to this article

Hot Product