Synthesis of Aristotelia-type alkaloids: Syntheses of the natural products (-)-serratenone and (+)-11,12-didehydromakonin-10-one

Article abstract of DOI:10.1002/1522-2675(200210)85:10<3400::AID-HLCA3400>3.0.CO;2-2

Two independent total syntheses of the Aristotelia alkaloid (-)-serratenone ((-)-1) are disclosed, one starting with (-)-α-pinene, the other one with (S)-α-terpineol. These correlations led to a revision of the originally proposed absolute configuration of the natural product. In the course of systematic investigations of the behavior of the indole alkaloids (+)-makomakine ((+)-18) and (-)-hobartine ((-)-22) towards oxidizing reagents, it was found that treatment with I₂ leads to no less than five different products. Depending on the exact reaction conditions, each of them can be obtained as the major component in yields between 40 and 60%. One of these compounds was shown to be identical with the natural product (+)-11,12-didehydromakonin-10-one ((+)-28).

Full text of DOI:10.1002/1522-2675(200210)85:10<3400::AID-HLCA3400>3.0.CO;2-2

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Helvetica Chimica Acta Vol. 85 (2002)
Synthesis of Aristotelia-Type Alkaloids
Part XVI1)
Syntheses of the Natural Products (À)-Serratenone and
(‡)-11,12-Didehydromakonin-10-one
by Renato Galli2), Markus Dobler2), Rolf G¸ller2), Reto Stahl3), and Hans-J¸rg Borschberg*
Laboratorium f¸r Organische Chemie der Eidgenˆssischen Technischen Hochschule, ETH Hˆnggerberg,
CH-8093 Z¸rich
Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday
Two independent total syntheses of the Aristotelia alkaloid (À)-serratenone ((À)-1) are disclosed, one
starting with (À)-a-pinene, the other one with (S)-a-terpineol. These correlations led to a revision of the
originally proposed absolute configuration of the natural product. In the course of systematic investigations of
the behavior of the indole alkaloids (‡)-makomakine ((‡)-18) and (À)-hobartine ((À)-22) towards oxidizing
reagents, it was found that treatment with I2 leads to no less than five different products. Depending on the exact
reaction conditions, each of them can be obtained as the major component in yields between 40 and 60%. One of
these compounds was shown to be identical with the natural product (‡)-11,12-didehydromakonin-10-one ((‡)-
28).
1. Introduction. The Aristotelia alkaloid (À)-serratenone ((À)-1) (Scheme 1) was
isolated by Bick and co-workers as an amorphous powder from Aristotelia serrata
W. R. B. Oliver where it occurs in concentrations ranging from 7 to 30 ppm [6][7]. The
proposed constitutional formula and relative configuration of this regular monoterpene
indole alkaloid was corroborated a few years later through a total synthesis of its
racemic form [8]. A peculiar feature of natural (À)-serratenone is that according to
circular dichroism (CD) evidence [9] its absolute configuration is opposite to the one
found for all other Aristotelia alkaloids (for reviews, see [10]). To clarify this point, a
stereoselective synthesis of (À)-1 was undertaken. Our retrosynthetic plan detailed in
Scheme 1 takes recourse to an acid-catalyzed cyclization of the intermediate imine 3,
which can be disconnected into protected (1H-indol-3-yl)acetaldehyde 4 and the p-
menth-1-en-8-ylamine derivative (À)-5. The latter can be traced back to (À)-trans-
verbenol ((À)-6), a building block of established absolute configuration derived from
the chiral pool [11].
2. Results and Discussion.
Following a procedure published by Gore and co-workers [12], we transformed (À)-
Synthesis of (À)-Serratenone, First Approach.
¬
1
)
)
)
Part XV: see [1].
Taken from the Ph.D. Theses of R . G.[2], M. D. [3], and R . G.[4].
Taken from the Diploma Thesis of R . S.[5].
2
3

Helvetica Chimica Acta Vol. 85 (2002)
3401
Scheme 1
Mps ˆ (4-methoxyphenyl)sulfonyl, Dfb ˆ 2,6-difluorobenzyl
trans-verbenol ((À)-6) into bromoacetal (À)-7 (Scheme 2). In our hands, reduction of
this intermediate with LiAlH4 according to the original procedure invariably gave a 1:2
mixture of (À)-8 and (‡)-9, the undesired major product evidently arising via an SN2'
process. This is in contrast with the claim that, under these conditions, only (À)-8 is
Scheme 2
a) N-Bromosuccinimide (NBS), acetone. b) See text. c) Py ¥ TsOH, EtOH. d) NaH, 2,6-difluorobenzyl
bromide, [15]crown-5, THF. e) HCOOH, 16 h at 238. f) Li, 4,4'-di(tert-butyl)biphenyl, THF, 2 h at À 708. g)
Pyridinium chlorochromate (PCC) on Al2O3, CH2Cl2. h) CHCl3/H2O, 6 d at 238.

3402
Helvetica Chimica Acta Vol. 85 (2002)
formed in 90% yield [12]. A comparison of the NMR data of our two products with the
one originally described for (À)-8 [12] showed that the earlier workers must actually
have isolated and characterized (‡)-9 instead. This conclusion was corroborated by a
1
long-range H/13C-HETCOR experiment performed on (‡)-9, which displayed all of
the expected relevant connectivities. In addition, the spectra of the two diols (À)-10 and
(‡)-11, resulting from hydrolysis of the acetonide groups of (À)-8 and (‡)-9,
respectively, were identical with the ones of racemic reference compounds, prepared
before via altogether different routes [8][13]. Fortunately, it turned out that a change
of the reducing agent from LiAlH4 to LiBHEt3 (Super HydrideTM) leads to the desired
compound (À)-8 as the single reaction product in over 90% yield.
The secondary OH group of diol (À)-10 was selectively protected as 2,6-
difluorobenzyl ether to furnish (À)-12. Recrystallization of this material served to
increase its optical purity from 78% to 93%. The transformation of (À)-12 into the final
target (À)-serratenone ((À)-1) closely followed the pathway developed for the racemic
series and proceeded with similar yields [8]. Whereas a comparison of the spectro-
scopic data (see Table and Exper. Part) of synthetic (À)-1 with the published values of
natural serratenone showed no significant discrepancies, there is a noticeable deviation
between the values of the optical rotation ([a]D ˆ À89.5 (c ˆ 0.29, CHCl3) for synthetic
vs. [a]D ˆ À45.3 (c ˆ 1, CHCl3) for natural (À)-1). Most likely, the lower value for
natural (À)-1 is caused by the presence of impurities that, at the same time, prevented
crystallization of the amorphous natural product, whereas we obtained the synthetic
sample in the form of colorless prisms, melting sharply at 184 1858. If correct, this
interpretation is tantamount to the conclusion that natural (À)-serratenone has the
same absolute configuration as all other Aristotelia alkaloids.
1
Table. Assignments of H-NMRChemical Shift Values d [ppm] in CDCl3
(À)-1 (‡)-18 (‡)-19 (À)-20 (À)-21 (À)-22 23
(À)-24 25
26
(‡)-27 (‡)-28
HÀC(2)
HÀC(5)
HÀC(6)
HÀC(7)
HÀC(8)
HÀC(10)
H'ÀC(10)
HÀC(11)
HÀC(14)
7.12
7.63
7.14
7.22
7.39
2.89
2.67
3.71
2.01
7.00
7.63
7.10
7.18
7.34
2.76
2.62
3.49
1.40
1.59
2.12
2.27
3.08
2.18
2.07
1.49
4.77
4.58
1.10
1.14
5.30
7.17
6.73
7.10
6.55
2.05
2.05
3.23
1.36
1.57
2.05
2.24
2.94
2.05
2.05
1.44
4.72
4.53
1.36
1.27
7.09
7.64
7.11
7.18
7.35
2.82
2.69
3.49
1.46
1.62
2.08
2.17
5.63
5.24
4.12 7.02
7.63 7.39 7.67
6.91 6.71 7.10
7.28 7.03 7.17
7.15 6.60 7.34
2.39 3.68
1.94 3.52
3.69
1.66 1.28 1.70
1.72 1.70 1.46
2.76 2.34 1.87
2.66 1.56 2.93
8.32
8.48
7.25
7.28
7.37
-
7.37
6.85
7.21
7.17
6.30
7.61
6.92
7.28
7.16
7.18 7.37
6.74 6.83
7.11 7.20
6.54 7.15
2.13 6.44
1.91
-
-
3.06
1.58
1.60
2.77
2.92
2.01
1.96
2.11
1.44
4.75
4.67
1.51
1.92
1.61
1.64
2.78
2.93
2.09
1.94
2.09
1.42
4.94
4.75
1.51
1.93
1.42 1.65
1.51 1.69
1.96 2.75
1.93 2.63
5.49 5.28
1.85
1.75
2.08
3.94
2.10
2.10
2.12
1.62
4.86
4.69
1.32
1.52
HantiÀC(15) 2.26
HsynÀC(15) 2.26
HÀC(16)
2.47
HendoÀC(18) 6.07
5.31
2.15
HexoÀC(18)
1.56 2.15
HendoÀC(19)
HexoÀC(19)
2.28
2.08
1.81
2.30 2.41
1.99 2.06
1.72 1.62
2.43 2.34 2.02
2.07 1.70 1.50
1.72 1.34 4.70
4.68
1.54 1.29 1.39
1.92 1.25 1.27
HÀC(20)
H'ÀC(20)
Me(21)
2.08
1.05
1.18
1.16
1.09
1.31 1.53
1.26 1.92
Me(22)

Helvetica Chimica Acta Vol. 85 (2002)
3403
Synthesis of (À)-Serratenone, Second Approach. In the course of systematic
investigations on the possibilities of oxidizing free or indole-protected Aristotelia
alkaloids [2], a much simpler route to (À)-serratenone (1) was uncovered (Scheme 3).
An acid-catalyzed CˆC isomerization of the readily obtainable indole-protected
makomakine 15 [14] led to the thermodynamically more stable hobartine derivative 16
in high yield [1]. Oxidation of the allylic CH2 group with CrO3/3,5-dimethyl-1H-
pyrazole [15] gave a 49% yield of indole-protected serratenone (À)-17, from which the
alkaloid (À)-1 could readily be obtained by reductive removal of the protective group.
Clearly, this second approach is superior to the method described above what length,
efficiency, and overall yields are concerned.
Scheme 3
a) HCl, H2O/AcOH, 40 min at 1108. b) CrO3, CH2Cl2, 3,5-dimethyl-1H-pyrazole. c) Na, naphthalene, THF.
Oxidation of (‡)-Makomakine ((‡)-18) and (À)-Hobartine ((À)-22) with Iodine.
Recently, we showed that I2 serves as a selective and effective oxidant for the
transformation of the pentacyclic Aristotelia alkaloid aristoteline into a variety of
natural products characterized by higher oxidation levels [16]. The same reagent was
also tested within the tetracyclic series [2], namely with the targets (‡)-makomakine
((‡)-18) and (À)-hobartine ((À)-22). In these cases, the results, displayed in Scheme 4,
tend to be less reproducible, and they depend critically on the exact reaction conditions.
Careful oxidation with 1 equiv. of I2 in MeOH led to the dehydrogenation products (‡)-
1
19 and 23, respectively. The H- and 13C-NMR spectra (see Table) point to unaltered
aliphatic subunits, but, in both cases, serious changes in the aromatic sections were
noticed. Obviously, the former indole chromophores had been replaced by o-
substituted aniline units. In addition, 1 equiv. of the solvent was incorporated into
the isolated products.
The fact that C(3) of (‡)-19 now appears as a s at 92.4 ppm indicates that the MeO group did enter in this
position. In the HETCOR spectrum of (‡)-19, a s at 5.30 ppm correlates with a d at 79.5 ppm, which is consistent
with C(2) now being substituted by two N-atoms. The relative configuration at the two new chiral centers were
established by NOE experiments: irradiation at 5.30 ppm led to enhanced 1H-NMR signals for HÀN(1),
MeOÀC(3), and Me(21).
The spectral data are fully compatible with the proposed structure (‡)-19.
Seemingly, the starting materials are attacked by I2 at their most nucleophilic position,

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Helvetica Chimica Acta Vol. 85 (2002)
Scheme 4
a) 1 Equiv. of I2, AcONa, MeOH. b) 5 Equiv. of I2, K2CO3, MeOH, CH2Cl2. c) 5.4 Equiv. of I2, AcONa, MeOH.
d) 3 Equiv. of I2, K2CO3, CHCl3/EtOH.

Helvetica Chimica Acta Vol. 85 (2002)
3405
i.e., C(3) [17], to give the 3-iodoindolenium species I, which then cyclizes to II4).
Afterwards, solvolysis under retention of configuration transforms the I-substituent
into a MeO group via an SN1 process to furnish (‡)-19 or 23, depending on the starting
material.
When (‡)-makomakine ((‡)-18) was treated with an excess of I2 and K2CO3 in
MeOH, the orange product (À)-20 was isolated in ca. 40% yield. The observed color is
caused by a long-wave UV maximum at 422 nm (log e 3.02). This points to a severe
alteration of the former indole chromophore, a fact borne out by the 13C-NMR
spectrum, in which an additional C-atom shows up in the aromatic region. The spectral
data confirmed the proposed structure of (À)-20.
The additional d for CH(10) of (À)-20 in the aromatic region appears at the expense of the formerly
aliphatic CH2(10) group. The original d of C(11) is replaced by a s at 105.2 ppm, and as the product is endowed
again with an additional MeO unit, this functional group must be located at C(11). In addition, the presence of
an axial MeO group at C(11) is evident due to the marked deshielding of the protons HantiÀC(15) (‡0.65 ppm as
compared to (‡)-18) and Me(21) (‡0.4 ppm) (see Table). The assumed configuration at C(11) was further
corroborated by a NOE experiment: irradiation of HÀC(10), which appears as a s at 6.30 ppm, led to enhanced
signals of HÀC(5) and of both H-atoms of the HÀC(20) group.
A compound with closely related spectroscopic properties, (À)-24, was isolated
when (À)-hobartine ((À)-22) was oxidized with excess I2 in CHCl3. However, in this
case, the substituent at C(11) was an EtO group which must have been introduced due
to the presence of ca. 1% of EtOH, which is commonly added to commercial CHCl3 as
a phosgene quencher.
Under similar conditions, but with sodium acetate as the base, both alkaloids were
transformed into the iodinated analogues (À)-21 and 25, respectively. Their spectro-
scopic properties (see Table and Exper. Part) closely resemble the ones of compounds
(À)-20 and (À)-24, apart from the now missing s of HÀC(10) and the additional s
accounting for this C-atom in the 13C-NMR spectra at the expense of the former d.
Possible mechanistic pathways to these compounds are sketched in Scheme 4 ( !
III VII). An attempt was made to prepare the putative intermediate III by an acid-
catalyzed elimination of MeOH from compound (‡)-19. However, the only product we
were able to isolate had an entirely different and unexpected structure (Scheme 5). Its
UV spectrum was almost identical with the one of o-toluidine and showed the
characteristic hypsochromic shift upon addition of acid. Extensive 2D-NMR experi-
ments (ROESY, NOSY, HETCOR, and HMBC)5) unambiguously led to structure 26
for this compound, which bears a strong resemblance to neohobartine, a by-product in
the acid-catalyzed cyclization of hobartine (22) to the pentacyclic alkaloid aristoteline
[19]. One of several possible pathways from (‡)-19 to 26 is displayed in Scheme 5 and
starts with an acid-mediated hydrolysis of the aminal grouping (VIII ! IX). The
following intramolecular iminium-ion condensation involving intermediate IX seems
unlikely for stereoelectronic reasons. However, this problem can be circumvented by
4
)
A compound with this partial structure was isolated in 81% yield by Pellegrini upon treating the
diketopiperazide prepared from 1-[(tert-butoxy)carbonyl]tryptophan and 2-(3,3-dimethylallyl)piperidine-
2-carboxylic acid with I2 and K2CO3 in THF [18].
The authors would like to thank Prof. B. Jaun (Laboratory for Organic Chemistry of the ETHZ) for
recording these spectra and for his help with their interpretation.
5
)

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Helvetica Chimica Acta Vol. 85 (2002)
Scheme 5
a) HBF4, AcOH, 1 h at 1008.
invoking intermediate X derived from IX by neighboring group participation.
Hydrolysis of the resulting vinylogous hemiaminal XI leads to XIII, which undergoes
an acid-catalyzed intramolecular etherification to yield the final product 26.
In an attempt to employ the reaction conditions that had been very successful in the
pentacyclic series [16], (‡)-makomakine ((‡)-18) was treated with I2 in CHCl3, which

Helvetica Chimica Acta Vol. 85 (2002)
3407
resulted in the formation of the known imine (‡)-27 [20] (Scheme 6). On the other
hand, oxidation of (‡)-18 with an excess of I2 in a two-phase system furnished the
natural product (‡)-11,12-didehydromakonin-10-one ((‡)-28) in 50% yield. This
compound was isolated from A. chilensis by Silva and co-workers in 1989 [21] and was
synthesized before via a different route [14]. To our disappointment, (À)-hobartine
((À)-22) failed to give any well-defined oxidation products upon similar treatment [5].
Scheme 6
a) 1. 1.3 Equiv. of I2, CHCl3; 2. Et3N. b) 1.3 Equiv. of I2, aq. NaHCO3 soln., CHCl3; 2. Et3N.
The authors would like to express their gratitude to the Swiss National Science Foundation for financial
support.
Experimental Part
General. Reagents and solvents were purchased from Fluka AG in the highest obtainable purity, unless
stated otherwise. CHCl3 and CDCl3 were passed through basic alumina (Woelm, act. I) immediately before use.
M. p. (not corrected): Tottoli apparatus, sealed evacuated capillaries. Optical rotations: Perkin-Elmer 241 at 258
and 589 nm (Nad). UV/VIS Spectra (lmax [nm], log e [dm3/mol ¥ cm]): Kontron Uvikon 869. IR: Perkin-Elmer
PE-781 spectrometer; nmax in cmÀ1
.
1H-NMR: d in ppm rel. to SiMe4 (ˆ0 ppm), J in Hz; 400 MHz: Bruker
AMX-400; 500 MHz: Bruker AMX-500. 13C-NMR: multiplicities from DEPT experiments; 100 MHz: Bruker
AMX-400; 125 MHz: Bruker AMX-500. NOE: Bruker WM-300 (300 MHz, CDCl3); irradiated proton !
affected signal(s). HETCOR: Varian Gemini-300 (300 MHz, CDCl3): cross peaks: d(C)/d(H). Mass spectra
(m/z [amu] (% base peak)): Hitachi-Perkin-Elmer, VG Tribrid; EI at 70 eV, unless stated otherwise; FAB in
3-nitrobenzyl alcohol as matrix.
(À)-(1R,6R)-3,3,5,5,9-Pentamethyl-2,4-dioxabicyclo[4.4.0]dec-8-ene ((À)-8). Method A: To a soln. of 7.90 g
(26.5 mmol) of (À)-76) in 200 ml of Et2O were added 1.5 equiv. of 1m LiBHEt3 (ˆsuper-HydrideTM; Fluka,
pract.) in THF at 08 over 30 min. After stirring for 15 h at 238, the mixture was cooled to 08 and treated with
27 ml of 2n aq. NaOH. After stirring for 4 h, the mixture was diluted with 200 ml of Et2O and extracted 3 times
with sat. aq. Na2CO3 soln. The org. phase was dried (K2CO3) and evaporated: 5.50 g (98.7%) of > 95% pure
1
(À)-8 (by H-NMR). Clear, slightly yellow oil. [a]D ˆ À22.6 (c ˆ 0.73, CHCl3). IR (CHCl3): 2995, 2910, 2850,
1450, 1438, 1378, 1364, 1303, 1261, 1195, 1190, 1122, 1052, 1000, 971, 947, 908, 824. 1H-NMR (400 MHz, CDCl3):
5.34 (m, 1 H); 3.95 (ddd, J ˆ 11.0, 9.3, 6.2, 1 H); 2.33 (ddm, J ˆ 16.6, 5.5, 1 H); 2.06 1.98 (m, 2 H); 1.76 (m, 1 H);
1.66 (br. s, 3 H); 1.61 (td, J ˆ 11.4, 5.2, 1 H); 1.49 (d, J ˆ 0.4, 3 H); 1.39 (d, J ˆ 0.5, 3 H); 1.28 (s, 3 H); 1.21 (s,
3 H). 13C-NMR (125 MHz, CDCl3): 131.5 (s); 119.7 (d); 97.7 (s); 73.5 (s); 65.4 (d); 44.5 (d); 37.2 (t); 32.3 (q);
6
)
Prepared from (À)-a-pinene (Aldrich, puriss.; 78% ee) according to [12].

3408
Helvetica Chimica Acta Vol. 85 (2002)
‡
31.3 (q); 25.6 (t); 24.8 (q); 24.3 (q); 23.2 (q). EI-MS: 195 (7, [M À 15] ), 153 (2), 136 (12), 135 (100), 119 (10),
107 (36), 94 (22), 93 (90), 91 (21), 85 (12), 79 (43), 77 (16), 59 (16), 43 (77).
Method B: To a suspension of LiAlH4 (9 mmol) in 20 ml of Et2O at 08 was added a soln. of 1.30 g
(4.36 mmol) of (À)-7 [12] in 10 ml of Et2O within 10 min. After stirring at 238 for 3 h, excess reagent was
destroyed by dropwise addition of H2O. Flash chromatography of the crude material (silica gel, petroleum ether/
Et2O 40 :1) furnished 198.3 mg (21.6%) of the minor product, identical with (À)-8 (see above), and 568.7 mg
(62%) of the main product (‡)-9. Data of (‡)-(1R,6R)-3,3,5,5,9-pentamethyl-2,4-dioxabicyclo[4.4.0]dec-9-ene
((‡)-9): Oil. [a]D ˆ ‡41.2 (c ˆ 0.41, CHCl3). IR (CHCl3): 2990, 2935, 2830, 1454, 1441, 1378, 1260, 1242, 1190,
1
1121, 1059, 1042, 1012, 969, 930, 904, 886, 810. H-NMR (500 MHz, CDCl3): 5.35 (m, 1 H); 4.30 (dm, J ˆ 9.8,
1 H); 2.09 (m, 1 H); 2.06 2.0 (m, 2 H); 1.97 (br. dd, J ˆ 17.1, 5.4, 1 H); 1.68 (br. s, 3 H); 1.64 (br. ddt, J ˆ 13.0,
5.9, 1.9, 1 H); 1.52 (ddd, J ˆ 12.9, 9.7, 2.4, 1 H); 1.50 (d, J ˆ 0.5, 3 H); 1.40 (d, J ˆ 0.6, 3 H); 1.27 (ddd, J ˆ 12.9,
11.6, 5.9, 1 H); 1.25 (s, 3 H); 1.22 (s, 3 H). 13C-NMR (125 MHz, CDCl3): 137.0 (s); 123.1 (d); 98.7 (s); 74.7 (s);
‡
66.3 (d); 46.5 (d); 32.1 (q); 30.9 (t); 30.3 (q); 24.8 (q); 23.1 (q); 23.0 (q); 21.9 (t). EI-MS: 210 (0.5, M ), 195 (27),
152 (23), 136 (10), 135 (100), 134 (25), 132 (16), 119 (49), 117 (17), 109 (21), 107 (13), 94 (34), 93 (36), 91 (35),
81 (27), 79 (35), 77 (16), 69 (22), 59 (12), 43 (40). According to its NMR data, this product is identical with
compound 4a in [12], which was erroneously assigned structure 8.
(À)-(4R,5R)-p-Menth-1-ene-5,8-diol ((À)-10). To a soln. of 6.40 g (30.4 mmol) of (À)-8 in 150 ml of EtOH
were added 1.2 g of pyridinium tosylate, and the mixture was kept at 238 for 14 h. After evaporation of most of
the solvent, the residue was distributed between CH2Cl2 and sat. aq. Na2CO3 soln. The org. phase was dried
(K2CO3) and evaporated: 5.18 g (100%) of (À)-10. Oil. [a]D ˆ À59.6 (c ˆ 1.01, CHCl3). IR (CHCl3): 3600, 3420,
2990, 2900, 2850, 1445, 1380, 1155, 1031, 912, 870, 828. 1H-NMR (400 MHz, CDCl3): 5.26 (m, 1 H); 3.98 (tm, J ˆ
9.9, 5.7, 1 H); 3.85 (br. s, 1 H); 3.60 (br. s, 1 H); 2.25 (br. dd, J ˆ 16.6, 5.7, 1 H); 2.16 2.06 (m, 2 H); 1.75 1.67
(m, 2 H); 1.65 (br. s, 3 H); 1.64 (td, J ˆ 11.4, 5.2, 1 H); 1.28 (s, 3 H); 1.20 (s, 3 H); max. deviation from the data of
(Æ)-10 [8]: Æ 0.01 ppm. 13C-NMR (125 MHz, CDCl3): 131.7 (s); 119.7 (d); 74.7 (s); 70.8 (d); 49.3 (d); 40.7 (t);
29.5 (q); 28.4 (t); 23.0 (q); 22.8 (q); max. deviation from the data of (Æ)-10 [8]: Æ 0.1 ppm. HETCOR (300/
75 MHz, CDCl3): 119.7/5.26; 70.8/3.98; 49.3/1.7; 40.7/2.25 and 2.1; 29.5/1.20; 28.4/2.1 and 1.7; 23.0/1.28; 22.8/1.65.
‡
EI-MS: 152 (10, [M À 18] ), 137 (19), 119 (30), 109 (100), 94 (75), 79 (91), 68 (21), 59 (77), 43 (41).
(‡)-(3R,4R)-p-Menth-1-ene-3,8-diol ((‡)-11). To a soln. of 1.20 g (5.7 mmol) of (‡)-9 in 45 ml of CHCl3
were added 5 ml of H2O, and the mixture was stirred at 238 for 6 days. The mixture was washed with 20 ml of sat.
aq. NaHCO3 soln., dried (K2CO3), and evaporated to yield 0.893 g of a slightly yellow oil. Chromatography
(silica gel, Et2O/petroleum ether 1:1) furnished 0.81 g of a colorless oil, which crystallized after trituration with
cold Et2O. M.p. 77 788 (hexane) ([13]: m.p. 768 for (Æ)-11). [a]D ˆ ‡57.2 (c ˆ 0.78, CHCl3) for material of
78% ee. IR, 1H- and 13C-NMR, and mass spectra: in agreement with those obtained earlier for (Æ)-11 [13].
(À)-(4R,5R)-5-[(2,6-Difluorobenzyl)oxy]-p-menth-1-en-8-ol ((À)-12). Prepared as described for racemic
material [8]. M.p. 77 788 (Et2O) ([8]: m.p. 928 for (Æ)-12). [a]D ˆ À110.8 (c ˆ 0.97, CHCl3) for material of
78% ee.
Upgrading of the Optical Purity of (À)-12. To a warm soln. of 11.0 g of (À)-12 (optical purity: 78%) in 10 ml
of Et2O were added 30 ml of petroleum ether (40 608). The clear soln. was inoculated with a single crystal of
(À)-12, and the mixture was kept at 238 for 84 h. The resulting cubic crystals were collected and dried at
0.002 Torr for 16 h to yield 7.4 g (67%) of a material with [a]D ˆ À132.4 (c ˆ 1.33, CHCl3) pointing to an optical
purity of 93%, which was confirmed by 1H-NMR (300 MHz, 1% in CDCl3 in the presence of tris{3-
[(heptafluoropropyl)hydroxymethylene]-(‡)-camphorato}europium(III) shift reagent (Aldrich, gold label)).
(À)-(4S,5R)-5-[(2,6-Difluorobenzyl)oxy]-p-menth-1-en-8-amine ((À)-5). Prepared as described for race-
mic material [8]. Oil. [a]D ˆ À68.2 (c ˆ 1.03, CHCl3) for material of 93% optical purity.
19-exo-[(2,6-Difluorobenzyl)oxy]-1-[(4-methoxyphenyl)sulfonyl]hobartine (ˆ(1S,4R,8R)-8-[(2,6-Di-
fluorobenzyl)oxy]-4-{{1-[(4-methoxyphenyl)sulfonyl]-1H-indol-3-yl}methyl}-2,2,6-trimethyl-3-azabicyclo[3.3.1]-
non-6-ene; 13). Prepared as described for racemic material [8]. Yield 30%, besides 42% of starting (À)-5. Pale-
yellow needles. M.p. 69 708 (CH2Cl2).
(À)-19-exo-Hobartin-19-ol (ˆ(1S,4R,8R)-4-(1H-Indol-3-ylmethyl)-2,2,6-trimethyl-3-azabicyclo[3.3.1]non-
6-en-8-ol; (À)-14). Prepared according to Method B in [8]. Yield 58%. Pale-rose needles. M.p. 98 1008 (Et2O).
[a]D ˆ À59.7 (c ˆ 1.33, CHCl3). UV (EtOH): 290 (3.58), 282 (3.67), 275 (sh, 3.63), 222 (4.41). IR, 1H- and
‡
13C-NMR data: identical with those of (Æ)-13 [8]. FAB-MS: 311 (100, [M ‡ 1] ), 293 (42), 289 (18), 199 (14),
181 (16), 180 (67), 159 (37), 130 (28), 107 (31), 89 (25), 77 (26), 57 (22).
(À)-Serratenone (ˆ(1S,4R)-4-(1H-Indol-3-ylmethyl)-2,2,6-trimethyl-3-azabicyclo[3.3.1]non-6-en-8-one;
(À)-1). Method A: To a soln. of 11.5 mg of (À)-14 in 10 ml of CH2Cl2 were added 165 mg of PCC on Al2O3,
freshly prepared according to [22] (content: ca. 6% of active CrVI). After stirring for 20 min, the mixture was

Helvetica Chimica Acta Vol. 85 (2002)
3409
filtered through Celite and the filtrate worked up with CH2Cl2 and sat. aq. Na2CO3 soln. to furnish 21.3 mg of
crude material. Chromatography (silica gel, CHCl3/MeOH/conc. aq. NH3 soln. 198 :2 :5) gave 8.1 mg (70%
yield) of (À)-1. Colorless prisms. M.p. 184 1858 (Et2O) ([6]: amorphous). [a]D ˆ À89.5 (c ˆ 0.29, CHCl3) ([6]:
[a]D ˆ À45.3 (c ˆ 1, CHCl3) for natural (À)-1). UV (EtOH): 290 (3.51), 282 (3.53), 222 (4.35). IR (CHCl3):
3480, 3310 (br.), 3060, 3040, 3005, 2930, 2800, 2855, 1659, 1651, 1620, 1456, 1388, 1431, 1419, 1375, 1338, 1310,
1301, 1179, 1091, 1030, 1011, 880. 1H-NMR (300 MHz, CDCl3): 8.04 (br. s, 1 H); 7.63 (dm, J ˆ 7.8, 1 H); 7.39 (dt,
J ˆ 8.1, 0.9, 1 H); 7.22 (ddd, J ˆ 8.1, 7.2, 1.2, 1 H); 7.14 (ddd, J ˆ 7.8, 7.1, 1.1, 1 H); 7.12 (d, J ˆ 2.5, 1 H); 6.07 (t, J ˆ
1.1, 1 H); 3.71 (ddd, J ˆ 8.6, 5.6, 2.6, 1 H); 2.89 (ddd, J ˆ 14.4, 5.6, 0.8, 1 H); 2.67 (ddd, J ˆ 14.4, 8.6, 0.8, 1 H);
2.47 (q, J ˆ 3.1, 1 H); 2.26 (t, J ˆ 3.1, 2 H); 2.08 (d, J ˆ 1.3, 3 H); 2.01 (t, J ˆ 3.0, 1 H); 1.18 (s, 3 H); 1.05 (s, 3 H);
deviations from natural (À)-1 [6]: at most Æ 0.03 ppm. 13C-NMR (75 MHz, CDCl3): 202.0 (s); 161.5 (s); 136.4
(s); 129.8 (d); 127.4 (s); 122.3 (2d); 119.5 (d), 118.8 (d); 112.9 (s); 111.3 (d); 52.8 (d); 50.91 (s); 50.88 (d); 40.9
‡
(d); 32.8 (t); 31.6 (t); 29.8 (q); 26.0 (q); 24.9 (q). EI-MS: 308 (40, M ), 293 (11), 200 (12), 199 (38), 183 (11), 179
(27), 178 (100), 159 (32), 158 (21), 144 (21), 143 (27), 131 (36), 130 (58), 117 (35), 110 (28), 88 (15), 81 (19), 80
(22), 78 (22), 58 (14), 43 (13).
Method B: To a cold (À408) soln. of 834 mg (1.74 mmol) of (À)-17 (see below) in 25 ml of THF (dist. from
K/benzophenone) was slowly added a deep-green soln. of Na/naphthalene, prepared by dissolving 1.13 g
(49.2 mmol) of Na and 6.4 g (49.9 mmol) of naphthalene in 95 ml of THF followed by stirring for 6 h at 238.
After addition of 18.2 ml of this reagent, the mixture stayed green, and the addition was stopped at once. The
mixture was quenched by adding 10 ml of sat. aq. NH4Cl soln. Workup with Et2O and sat. aq. Na2CO3 soln.,
followed by chromatography (silica gel, CH2Cl2/MeOH 24 :1) furnished 327 mg (61%) of (À)-1, indistinguish-
able from the sample prepared according to Method A.
1-[(4-Methoxyphenyl)sulfonyl]hobartine (ˆ(1S,4R)-4-{{1-[(4-Methoxyphenyl)sulfonyl]-1H-indol-3-yl}-
methyl}-2,2,6-trimethyl-3-azabicyclo[3.3.1]non-6-ene; 16). A soln. of 1.0 g (2.16 mmol) of 15 [14] in 80 ml of
AcOH, 200 ml of H2O and 200 ml of 37% aq. HCl soln. was refluxed for 40 min, cooled to 08 and then poured
into 30% aq. NaOH soln. The mixture having now pH 10 was extracted with CH2Cl2 (3Â). The combined org.
extracts were dried (K2CO3) and evaporated: 930 mg (93%) of 16. Colorless foam. IR (CHCl3): 3030, 3005,
2910, 2840, 1593, 1578, 1494, 1460, 1444, 1364, 1300, 1260, 1182, 1162, 1128, 1119, 1097, 1018, 971, 828. 1H-NMR
(400 MHz, CDCl3): 7.99 (dm, J ˆ 8.2, 1 H); 7.78 (m, 2 H); 7.48 (dm, J ˆ 7.7, 1 H); 7.44 (s, 1 H); 7.30 (ddd, J ˆ 8.3,
7.3, 1.2, 1 H); 7.22 (ddd, J ˆ 8.2, 7.4, 1.1, 1 H); 6.85 (m, 2 H); 5.63 (m, 1 H); 3.78 (s, 3 H); 3.38 (td, J ˆ 7.3, 2.3,
1 H); 2.67 (ddd, J ˆ 15.1, 6.7, 0.9, 1 H); 2.54 (ddd, J ˆ 15.1, 7.6, 1.1, 1 H); 2.26 (br. d, J ˆ 18.5, 1 H); 2.11 2.05 (m,
3 H); 1.72 (q, J ˆ 1.9, 3 H); 1.61 (dt, J ˆ 12.5, 3.1, 1 H); 1.47 (m, 1 H); 1.15 (s, 3 H); 1.09 (s, 3 H). 13C-NMR
(100 MHz, CDCl3): 163.7 (s); 135.2 (s); 132.2 (s); 131.0 (s); 129.7 (s); 129.0 (2 d); 125.9 (d); 124.7 (d), 123.5 (d);
123.1 (d); 119.8 (s); 119.6 (d); 114.4 (2d); 113.7 (d); 55.6 (q); 55.5 (s); 54.1 (d); 36.7 (d); 34.8 (d); 29.7 (t); 28.9
‡
(q); 28.7 (t); 27.6 (t); 25.6 (q); 25.1 (q). EI-MS: 464 (0.5, M ), 449 (2), 293 (5), 171 (9), 165 (16), 164 (100), 130
(11), 93 (9).
1-[(4-Methoxyphenyl)sulfonyl]serratenone (ˆ(1S,4R)-4-{{1-[(4-Methoxyphenyl)sulfonyl]-1H-indol-3-yl}-
methyl}-2,2,6-trimethyl-3-azabicyclo[3.3.1]non-6-en-8-one; (À)-17). To a suspension of 2.79 g (27.9 mmol) of
CrO3 (Fluka, puriss.) in 45 ml of CH2Cl2 were added 2.80 g (29.1 mmol) of 3,5-dimethyl-1H-pyrazole (Fluka,
puriss.) at À 208. To the resulting brown-orange mixture was added within 5 min a soln. of 1.30 g (2.8 mmol) of
16 in 5 ml of CH2Cl2 at À 208. After stirring at À 208 for 7 h, there were added 50 ml of 5n aq. NaOH, and
stirring was continued for 16 h. The mixture was worked up with CH2Cl2 and chromatographed (silica gel,
CH2Cl2/AcOEt 1:1): 651 mg (49%) of (À)-17. White foam. [a]D ˆ À114 (c ˆ 0.51, CHCl3). IR (CHCl3): 3010,
2980, 2940, 1659, 1598, 1498, 1447, 1373, 1264, 1167, 1130, 1099, 1032, 977, 834. 1H-NMR (400 MHz, CDCl3): 8.01
(dm, J ˆ 8.3, 1 H); 7.78 (m, 2 H); 7.48 (dm, J ˆ 7.8, 1 H); 7.45 (s, 1 H); 7.33 (ddd, J ˆ 8.3, 7.2, 1.1, 1 H); 7.25 (ddd,
J ˆ 7.8, 7.1, 1.1, 1 H); 7.12 (d, J ˆ 2.5, 1 H); 6.07 (t, J ˆ 1.1, 1 H); 3.71 (td, J ˆ 7.5, 1.0, 1 H); 6.86 (m, 2 H); 6.05 (t,
J ˆ 1.1, 1 H); 3.78 (s, 3 H); 3.61 (ddd, J ˆ 8.6, 5.6, 2.7, 1 H); 2.74 (ddd, J ˆ 14.9, 5.6, 0.9, 1 H); 2.53 (ddd, J ˆ 14.9,
8.6, 1.0, 1 H); 2.40 (q, J ˆ 2.7, 2 H); 2.30 2.21 (m, 2 H); 2.00 (m, 1 H); 2.00 (d, J ˆ 1.4, 3 H); 1.35 (br. s, 1 H); 1.16
(s, 3 H); 1.03 (s, 3 H). 13C-NMR (100 MHz, CDCl3): 201.7 (s); 163.7 (s); 160.8 (s); 135.4 (s); 130.8 (s); 129.7 (s);
128.9 (2 d); 124.9 (d); 123.8 (d), 123.2 (d); 119.6 (s); 114.4 (2d); 114.0 (d); 55.6 (q); 52.1 (d); 50.7 (s); 50.5 (d);
‡
40.7 (d); 32.6 (t); 31.0 (t); 29.7 (q); 25.8 (q); 24.9 (q). EI-MS: 479 (38), 478 (3, M ), 369 (14), 309 (23), 252 (10),
199 (38), 198 (11), 179 (10), 178 (79), 162 (14), 140 (100), 131 (21), 130 (46), 108 (25), 58 (23).
(‡)-2,3-Dihydro-3-methoxy-2,12-cyclomakomakine (ˆ(1S,4S,8R,10R)-8-Methoxy-2,2-dimethyl-12-methyl-
enebenzo[6,7]-3,5-diazatetracyclo[9.3.1.03,1004,8]pentadecane; (‡)-19). To a cold (À158) soln. of 74.7 mg
(0.25 mmol) of synthetic (‡)-makomakine ((‡)-18) [14] and 433 mg (5.27 mmol) of NaOAc in 10 ml of
MeOH was added a soln. of 59 mg (0.23 mmol) of I2 in 14 ml of MeOH over 2 h. The stirred mixture was
allowed to reach 238 within 2 h and was then quenched by adding 2 ml of sat. aq. Na2S2O3 soln. Workup with

3410
Helvetica Chimica Acta Vol. 85 (2002)
CH2Cl2 and 1m aq. NaHCO3 soln., followed by chromatography (silica gel, hexane/AcOEt 10 :1 ! 2 :1)
furnished 35 mg (43%) of colorless crystals. M.p. 140 1418. [a]D ˆ ‡286 (c ˆ 0.1, EtOH). UV (EtOH):
308 (3.45), 246 (3.98). UV (EtOH, 1 drop of conc. H2SO4): 298 (3.21), 239 (3.76). IR (CHCl3): 3400 (br.), 3060,
3000, 2930, 2860, 2820, 1641, 1609, 1483, 1467, 1455, 1380, 1361, 1312, 1298, 1239, 1161, 1112, 1093, 1081, 1058,
1017, 999, 978, 888. 1H-NMR (400 MHz, CDCl3): 7.17 (ddd, J ˆ 7.4, 1.3, 0.6, 1 H); 7.10 (ddd, J ˆ 7.8, 7.4, 1.3, 1 H);
6.73 (td, J ˆ 7.4, 1.0, 1 H); 6.55 (ddd, J ˆ 7.8, 1.0, 0.6, 1 H); 5.30 (s, 1 H); 4.72 (t, J ˆ 2.4, 1 H); 4.53 (t, J ˆ 2.4, 1 H);
3.85 (br. s, 1 H); 3.23 (ddd, J ˆ 10.0, 5.9, 3.4, 1 H); 3.09 (s, 3 H); 2.94 (tdt, J ˆ 13.7, 6.0, 2.7, 1 H); 2.24 (br. q,
J ˆ 2.9, 1 H); 2.11 1.95 (m, 5 H); 1.57 (dt, J ˆ 12.8, 3.2, 1 H); 1.44 (tdd, J ˆ 13.7, 6.0, 4.2, 1 H); 1.36 (s, 3 H);
1.36 (m, 1 H); 1.27 (s, 3 H). NOE (300 MHz, CDCl3): 5.30 (HÀC(2)) ! 3.85 (HÀN), 3.09 (MeO), 1.36
(Me(21)), and, at the limit of significance, 3.23 (HÀC(11)) and 2.94 (HendoÀC(18)); 3.09 (MeO) ! 7.17
(HÀC(5)) and 5.30 (HÀC(2)). 13C-NMR (100 MHz, CDCl3): 151.2 (s); 150.8 (s); 129.4 (d); 128.2 (s); 124.6 (d);
118.3 (d), 109.2 (d); 108.6 (t); 92.4 (s); 79.5 (d); 56.1 (d); 55.0 (s); 52.5 (q); 43.0 (t); 42.2 (d); 40.6 (d); 32.0 (t);
31.3 (t); 29.0 (t); 27.1 (q); 25.2 (q). HETCOR (300/75 MHz, CDCl3): 129.4/7.10; 128.2/7.17; 124.6/6.73; 118.3/
6.55; 108.6/4.72 and 4.53; 79.5/5.30; 56.1/3.23; 52.5/3.09; 43.0/2.02 (2Â); 42.2/2.24; 40.6/1.36; 32.0/2.02 and 1.57;
‡
31.3/2.94 and 2.01; 29.0/2.01 and 1.44; 27.1/1.36; 25.2/1.27. EI-MS: 324 (14, M ), 310 (22), 309 (100), 293 (11), 290
(28).
(À)-1,10-Didehydro-11-methoxy-2,12-cyclomakomakine (ˆ(1S,10S)-10-Methoxy-2,2-dimethyl-12-methyl-
enebenzo[6,7]-3,5-diazatetracyclo[9.3.1.03,1004,8]pentadeca-4,8-diene; (À)-20). To a soln. of 113 mg (0.38 mmol)
of (‡)-makomakine (18) [14] in 20 ml of CH2Cl2 were added 380 mg (2.75 mmol) of K2CO3 and 0.5 ml of MeOH
and then 484 mg (1.91 mmol) of I2. After stirring for 1 h at 238, the mixture was poured on 20 ml of 1m aq.
Na2S2O3 and extracted with 30 ml of CH2Cl2 (3Â). The combined org. extract was dried (K2CO3) and
evaporated and the crude product chromatographed (silica gel, hexane/AcOEt 10 :1): 49 mg (40%) of 20.
Orange foam. [a]D ˆ À70 (c ˆ 0.05, EtOH). UV (EtOH): 422 (3.02), 303 (3.31), 260 (4.69), 254 (4.67). UV
(EtOH, 1 drop of conc. H2SO4): 376 (3.09), 308 (3.62), 246 (4.02). IR (CHCl3): 3070, 3050, 3000, 2960, 2930,
1
1581, 1562, 1442, 1426, 1388, 1297, 1185, 1169, 1143, 1116, 1080, 1067, 1043. H-NMR (400 MHz, CDCl3): 7.37
(dm, J ˆ 7.3, 1 H); 7.21 (ddd, J ˆ 7.9, 7.2, 1.3, 1 H); 7.17 (ddd, J ˆ 7.9, 1.4, 0.7, 1 H); 6.85 (td, J ˆ 7.2, 1.4, 1 H); 6.30
(s, 1 H); 4.75 (t, J ˆ 2.1, 1 H); 4.67 (t, J ˆ 2.1, 1 H); 3.10 (s, 3 H); 2.92 (m, 1 H); 2.77 (dm, J ˆ 12.9, 1 H); 2.14
1.93 (m, 3 H); 1.92 (s, 3 H); 1.61 1.55 (m, 2 H); 1.51 (s, 3 H); 1.44 (tdd, J ˆ 13.5, 6.4, 2.9, 1 H). NOE (300 MHz,
CDCl3): 6.30 (HÀC(10)) ! 7.37 (HÀC(5)), 4.75 (HÀC(20)), 4.67 (H'ÀC(20)), 3.10 (MeO), and 2.92
(HÀC(16)); 3.10 (MeO) ! 6.30 (HÀC(10)) and 1.51 (Me(21)). 13C-NMR (100 MHz, CDCl3): 173.0 (s); 166.6
(s); 146.0 (s); 140.6 (s); 131.1 (2d); 123.3 (d); 122.2 (s); 120.9 (d), 117.7 (d); 111.5 (t); 105.2 (s); 58.7 (s); 49.8 (q);
‡
46.7 (d); 38.9 (d); 28.6 (t); 28.2 (t); 27.7 (t); 27.6 (q); 27.4 (q). EI-MS: 320 (44, M ), 305 (58), 291 (22), 290 (100),
289 (70), 288( 22), 273 (16), 247 (18), 245 (20), 220 (30), 219 (48), 207 (24), 185 (69), 171 (61), 156 (27), 155
(26).
(À)-1,10-Didehydro-10-iodo-11-methoxy-2,12-cyclomakomakine (ˆ(1S,10R)-9-Iodo-10-methoxy-2,2-di-
methyl-12-methylenebenzo[6,7]-3,5-diazatetracyclo[9.3.1.03,10.04,8]pentadeca-4,8-diene; (À)-21). To a soln. of
22 mg (0.075 mmol) of (‡)-makomakine (18) [14] in 3 ml of MeOH were added 100 mg (1.22 mmol) of NaOAc
and 102 mg (0.40 mmol) of I2. After stirring for 1 h at 238, the mixture was poured on 20 ml of 1m aq. Na2S2O3
soln. and extracted with 30 ml of CH2Cl2 (3Â). The combined org. extract was dried (K2CO3) and evaporated
and the crude product chromatographed (silica gel, hexane/AcOEt 85 :15): 15 mg (44%) of 21. Orange foam.
[a]D ˆ À128 (c ˆ 0.06, EtOH). UV (EtOH): 431 (3.04), 328 (3.84), 260 (4.69), 316 (9.92), 260 (4.50). UV
(EtOH, 1 drop of conc. H2SO4): 386 (3.33), 328 (3.99). IR (CHCl3): 3070, 3040, 3000, 2960, 2930, 1581, 1561,
1441, 1428, 1381, 1285, 1187, 1161, 1145, 1114, 1080, 1069, 1011. 1H-NMR (400 MHz, CDCl3): 7.61 (ddd, J ˆ 7.3,
1.3, 0.6, 1 H); 7.28 (td, J ˆ 7.7, 1.4, 1 H); 7.16 (dt, J ˆ 7.9, 0.8, 1 H); 6.92 (td, J ˆ 7.4, 1.0, 1 H); 4.94 (t, J ˆ 2.0, 1 H);
4.75 (t, J ˆ 2.0, 1 H); 3.05 (s, 3 H); 2.93 (m, 1 H); 2.78 (dq, J ˆ 12.7, 2.9, 1 H); 2.15 2.02 (m, 2 H); 1.96 1.92
(m, 4 H, incl. 1.93 (s, 3 H)); 1.65 1.55 (m, 2 H); 1.51 (s, 3 H); 1.42 (m, 1 H). 13C-NMR (100 MHz, CDCl3):
170.9 (s); 165.8 (s); 147.1 (s); 144.3 (s); 131.9 (d); 122.7 (d); 122.5 (s); 120.9 (d), 117.9 (d); 113.4 (t); 104.6 (s);
‡
101.5 (s); 59.8 (s); 49.6 (q); 46.1 (d); 39.3 (d); 28.8 (t); 28.1 (t); 27.73 (q); 27.70 (t); 27.4 (q). EI-MS: 446 (40, M ),
431 (35), 417 (22), 416 (100), 415 (43), 319 (29), 311 (31), 297 (19), 289 (14), 287 (11), 245 (16), 219 (18), 183
(12).
2,3-Dihydro-3-methoxy-2,12-cyclohobartine (ˆ(1S,4S,8R,10R)-8-Methoxy-2,2,12-trimethyl-benzo[6,7]-3,5-
diazatetracyclo[9.3.1.03,10.04,8]pentadec-12-ene; 23). To a cold (À408) soln. of 22.5 mg (0.076 mmol) of synthetic
(À)-hobartine (22) [23] and 74.6 mg (0.91 mmol) of NaOAc in 5 ml of MeOH was added a soln. of 15.4 mg
(0.061 mmol) of I2 in 5 ml of MeOH over 40 min. The stirred mixture was allowed to reach 238 within 2 h and
was then quenched by adding 3 ml of 1m aq. Na2S2O3. Workup with CH2Cl2 and 1m aq. NaHCO3, followed by
chromatography (silica gel, hexane/AcOEt 10 :1 ! 1:1) furnished 11.3 mg (46%) of 23. White foam. IR

Helvetica Chimica Acta Vol. 85 (2002)
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(CHCl3): 3420 (br.), 3050, 3000, 2930, 2825, 1610, 1483, 1468, 1380, 1361, 1312, 1298, 1251, 1239, 1169, 1110, 1083,
1010, 960. 1H-NMR (500 MHz, CDCl3): 7.18 (ddd, J ˆ 7.4, 1.3, 0.6, 1 H); 7.11 (ddd, J ˆ 7.8, 7.4, 1.3, 1 H); 6.74 (td,
J ˆ 7.4, 0.9, 1 H); 6.54 (dm, J ˆ 7.8, 1 H); 5.49 (m, 1 H); 5.24 (s, 1 H); 3.90 (br. s, 1 H); 3.06 (dt, J ˆ 11.2, 3.9, 1 H);
3.04 (s, 3 H); 2.30 (dm, J ˆ 18.9, 1 H); 2.13 (dd, J ˆ 11.0, 4.4, 1 H); 2.01 1.90 (m, 4 H); 1.72 (q, J ˆ 2.0, 3 H); 1.51
(dt, J ˆ 12.1, 3.0, 1 H); 1.42 (m, 1 H); 1.31 (s, 3 H); 1.26 (s, 3 H). 13C-NMR (125 MHz, CDCl3): 151.6 (s); 133.4
(s); 129.6 (d); 127.7 (s); 124.7 (d); 124.0 (d); 118.2 (d), 108.9 (d); 92.3 (s); 79.6 (d); 56.2 (d); 55.1 (s); 52.4 (q);
43.5 (t); 39.8 (d); 37.1 (d); 27.5 (2t); 27.4 (q); 25.5 (q); 24.6 (q).
(À)-1,10-Didehydro-11-ethoxy-2,12-cyclohobartine (ˆ(1S,10S)-10-Ethoxy-2,2,12-trimethyl-benzo[6,7]-3,5-
diazatetracyclo[9.3.1.03,10.04,8]pentadeca-4,8,12-triene; (À)-24). To a soln. of 108 mg (0.37 mmol) of (À)-
hobartine (22) [23] in 6 ml of CHCl3 containing 1% of EtOH as stabilizer were added 104 mg (0.75 mmol) of
K2CO3 and 268 mg (1.05 mmol) of I2. After stirring for 6 h at 238, an additional 97 mg (0.7 mmol) of K2CO3 were
added, and stirring was continued for 2 h. Then the mixture was poured on 20 ml of 1m aq. Na2S2O3 and
extracted with 30 ml of CH2Cl2 (3Â). The combined org. extract was dried (K2CO3) and evaporated and the
crude product chromatographed (silica gel, hexane/AcOEt 2 :1): 48 mg (39%) of 24. Orange foam. [a]D ˆ À380
(c ˆ 0.07, EtOH). UV (EtOH): 418 (3.00), 255 (4.59). UV (EtOH, 1 drop of conc. H2SO4): 372 (3.08). IR
(CHCl3): 3050, 3000, 2970, 2930, 1613, 1581, 1558, 1440, 1428, 1386, 1318, 1293, 1189, 1171, 1160, 1148, 1114,
1095, 1056. 1H-NMR (400 MHz, CDCl3): 7.37 (dm, J ˆ 7.2, 1 H); 7.20 (td, J ˆ 7.6, 1.3, 1 H); 7.15 (dm, J ˆ 7.9, 1 H);
6.83 (td, J ˆ 7.3, 1.3, 1 H); 6.44 (s, 1 H); 5.28 (m, 1 H); 3.37 (m, 2 H); 2.75 (dm, J ˆ 12.6, 1 H); 2.63 (m, 1 H); 2.41
(dm, J ˆ 19.4, 1 H); 2.06 (dm, J ˆ 19.4, 1 H); 1.92 (s, 3 H); 1.69 (dt, J ˆ 12.6, 3.1, 1 H); 1.65 (m, 1 H); 1.62 (m,
3 H); 1.53 (s, 3 H); 1.19 (t, J ˆ 7.0, 3 H). 13C-NMR (100 MHz, CDCl3): 173.1 (s); 167.0 (s); 140.1 (s); 131.1 (s);
131.0 (d); 130.9 (d); 124.8 (d), 123.0 (d); 122.2 (s); 120.4 (d); 117.5 (d); 106.4 (s); 59.1 (s); 58.7 (t); 43.4 (d); 37.5
(d); 28.3 (q); 27.7 (q); 27.3 (t); 25.3 (q); 23.7 (t); 15.1 (q). HETCOR (200/50 MHz, CDCl3): 131.0/6.44; 130.9/
7.20; 124.8/5.28; 123.0/7.37; 120.4/6.83; 117.5/7.15; 58.7/3.37; 43.4/2.63; 37.5/1.63; 28.3/1.92; 27.7/1.53; 27.3/2.41 and
‡
2.06; 25.3/1.62; 23.7/2.75 and 1.69; 15.1/1.19. EI-MS: 334 (34, M ), 306 (22), 305 (100), 290 (28), 219 (7), 211 (7),
172 (11), 171 (87).
1,10-Didehydro-10-iodo-11-methoxy-2,12-cyclohobartine (ˆ(1S,10R)-9-Iodo-10-methoxy-2,2,12-trimethyl-
benzo[6,7]-3,5-diazatetracyclo[9.3.1.03,10.04,8]pentadeca-4,8,12-triene; 25). To a soln. of 22 mg (0.074 mmol) of
(À)-hobartine (22) [23] in 3 ml of MeOH were added 113 mg (1.37 mmol) of NaOAc and 102 mg (0.40 mmol) of
I2. After stirring for 6 h at 238, the mixture was quenched by adding 3 ml of 1m aq. Na2S2O3 and 20 ml of 1m aq.
NaHCO3 and was then extracted with 30 ml of CH2Cl2 (3Â). The combined org. extract was dried (K2CO3) and
evaporated and the crude product chromatographed (silica gel, hexane/AcOEt 85 :15): 21 mg (63%) of 25.
Orange foam. IR (CHCl3): 3000, 2960, 2835, 1614, 1580, 1561, 1442, 1428, 1379, 1320, 1284, 1253, 1094, 1066,
1049, 1011. 1H-NMR (400 MHz, CDCl3): 7.63 (ddd, J ˆ 7.3, 1.3, 0.6, 1 H); 7.28 (td, J ˆ 7.7, 1.3, 1 H); 7.15 (dt, J ˆ
7.8, 0.8, 1 H); 6.91 (td, J ˆ 7.4, 1.0, 1 H); 5.31 (m, 1 H); 3.08 (s, 3 H); 2.76 (dm, J ˆ 13.0, 1 H); 2.66 (t, J ˆ 2.9, 1 H);
2.43 (dm, J ˆ 19.4, 1 H); 2.07 (dm, J ˆ 19.4, 1 H); 1.92 (s, 3 H); 1.72 (m, 3 H); 1.72 (dt, J ˆ 12.5, 3.0, 1 H); 1.66 (m,
1 H); 1.54 (s, 3 H). 13C-NMR (100 MHz, CDCl3): 171.1 (s); 166.2 (s); 147.3 (s); 131.9 (d); 130.7 (s); 125.8 (d);
122.6 (d), 122.4 (s); 120.6 (d); 117.8 (d); 107.4 (s); 101.0 (s); 60.3 (s); 50.1 (q); 42.6 (d); 37.9 (d); 28.2 (q); 27.8 (q);
27.7 (t); 26.3 (q); 23.9 (t).
17,20-Dihydro-3,17-epoxyneohobartine (ˆ2-[(1S)-4,4,8-Trimethyl-3-aza-12-oxapentacyclo[6.3.15,9.02,7.03,10]-
tridec-1-yl]benzenamine; 26). To a soln. of 77.5 mg (0.24 mmol) of (‡)-19 in 1 ml of AcOH were added 10 ml of
48% aq. HBF4 soln. The mixture was heated to 1008 for 1 h and then poured on ice. The mixture was rendered
basic by adding conc. aq. NH3 soln. and extracted with 30 ml of CH2Cl2 (3Â). The combined org. extract was
dried (K2CO3) and evaporated and the crude product chromatographed (silica gel, AcOEt/MeOH 5 :1): 27.7 mg
(37%) of 26. White powder. IR (CHCl3): 3480, 3360, 3230, 2990, 2960, 2920, 2900, 1633, 1610, 1578, 1491, 1452,
1381, 1374, 1303, 1295, 1262, 1130, 1121, 1099, 1060, 1034, 1012. 1H-NMR (400 MHz, CDCl3): 7.39 (dd, J ˆ 7.7, 1.6,
1 H); 7.03 (ddd, J ˆ 7.6, 7.3, 1.6, 1 H); 6.71 (td, J ˆ 7.5, 1.2, 1 H); 6.60 (dd, J ˆ 7.9, 1.2, 1 H); 4.27 (br. s, 2 H); 4.12
(dm, J ˆ 4.2, 1 H); 3.69 (dm, J ˆ 3.7, 1 H); 2.39 (dd, J ˆ 11.4, 4.5, 1 H); 2.34 (ddt, J ˆ 13.7, 3.9, 3.1, 1 H); 2.16 (dq,
J ˆ 13.7, 3.1, 1 H); 1.94 (d, J ˆ 11.4, 1 H); 1.74 1.68 (m, 2 H); 1.57 1.56 (m, 2 H); 1.34 (s, 3 H); 1.29 (s, 3 H); 1.28
(m, 1 H); 1.25 (s, 3 H). 13C-NMR (100 MHz, CDCl3): 143.9 (s); 127.6 (d); 126.0 (s); 125.7 (d); 117.4 (d); 115.9
(d); 88.3 (s), 83.4 (s); 66.8 (d); 59.6 (d); 53.7 (s); 43.4 (t); 42.4 (d); 37.8 (d); 31.0 (d); 29.0 (t); 27.6 (q); 26.5 (t);
26.4 (q); 20.8 (q). HETCOR (300/75 MHz, CDCl3): 127.6/7.03; 125.7/7.39; 117.4/6.71; 115.9/6.60; 66.8/4.12; 59.6/
3.69: 43.4/2.39 and 1.94; 42.4/1.56; 37.8/1.56; 31.0/1.28; 29.0/2.16 and 1.7; 27.6/1.29; 26.5/2.16 and 1.7; 26.4/1.25;
20.8/1.34. HMBC (300 MHz, CDCl3): 143.9/7.39 and 7.03; 127.6/7.39; 126.0/6.71 and 6.60; 125.7/7.03; 117.4/6.60;
115.9/6.71; 88.3/7.39, 3.69 and 1.94; 83.4/4.12, 3.69, 2.39, 2.16 and 1.34; 66.8/3.69, 1.94 and 1.7; 59.6/4.12, 2.39 and
‡
1.7; 53.7/1.7, 1.29 and 1.25; 43.4/4.12; 42.4/1.34; 37.8/2.39 and 1.34; 31.0/1.29 and 1.25. EI-MS: 310 (68, M ), 295

3412
Helvetica Chimica Acta Vol. 85 (2002)
(30), 199 (14), 190 (45), 176 (17), 158 (11), 146 (21), 130 (52), 120 (100), 93 (34), 92 (48), 77 (33), 65 (37), 58
(65), 43 (40), 42 (25), 41 (49).
(‡)-11,12-Didehydromakomakine (ˆ(5S)-2-(1H-Indol-3-ylmethyl)-4,4-dimethyl-8-methylene-3-azabicy-
clo[3.3.1]non-2-ene; (‡)-27). To a soln. of 201.5 mg (0.68 mmol) of synthetic (‡)-makomakine ((‡)-18) in
7 ml of CHCl3 were added 261.3 mg (1.03 mmol) of I2. After stirring at 238 for 75 h, Et3N (0.08 ml) was added.
The mixture was poured onto 60 ml of H2O and 6 ml of conc. aq. NH3 soln. and extracted with 100 ml of CHCl3
(3Â). The combined org. extract was dried (K2CO3) and evaporated and the crude product chromatographed
(silica gel, CHCl3/Et2O/Et2NH 80 :20 :1): 114 mg (57%) of (‡)-27. White powder. M.p. 100 1088. [a]D ˆ ‡188
(c ˆ 1.3, CHCl3). UV (EtOH): 314 (3.42), 291 (3.54), 266 (3.70). IR (CHCl3): 3480, 3070, 3000, 2935, 1629,
1518, 1456, 1421, 905. 1H-NMR (500 MHz, CDCl3): 8.22 (br. s, 1 H); 7.67 (dm, J ˆ 8.1, 1 H); 7.34 (dt, J ˆ 8.1, 0.9,
1 H); 7.17 (dddd, J ˆ 8.1, 7.2, 1.2, 0.3, 1 H); 7.10 (ddd, J ˆ 7.9, 7.1, 1.0, 1 H); 7.02 (m, 1 H); 4.70 (t, J ˆ 2.0, 1 H);
4.68 (t, J ˆ 2.0, 1 H); 3.68 (d, J ˆ 14.4, 1 H); 3.52 (dd, J ˆ 14.4, 1.2, 1 H); 2.93 (m, 1 H); 2.18 1.99 (m, 2 H); 2.02
(dm, J ˆ 13.5, 1 H); 1.87 (dq, J ˆ 12.4, 3.1, 1 H); 1.70 (m, 1 H); 1.50 (tdd, J ˆ 13.5, 5.8, 3.9, 1 H), 1.46 (ddd, J ˆ
12.4, 3.4, 2.2, 1 H); 1.39 (s, 3 H); 1.27 (s, 3 H); deviations from reported chemical shifts [20b] at most Æ
0.04 ppm. 13C-NMR (125 MHz, CDCl3): 167.9 (s); 148.5 (s); 136.4 (s); 127.9 (s); 122.7 (d); 121.9 (d); 119.5 (d),
119.3 (d); 112.2 (s); 111.0 (d); 108.6 (t); 58.0 (s); 42.4 (d); 35.5 (t); 35.4 (d); 31.5 (q); 30.0 (t); 29.8 (t); 29.2 (t);
‡
27.2 (q); deviations from reported chemical shifts [20b] at most Æ 0.2 ppm. EI-MS: 292 (90, M ), 277 (10), 220
(15), 205 (30), 156 (100), 130 (17), 93 (17).
(‡)-11,12-Didehydromakomakin-10-one (ˆ(5S)-4,4-Dimethyl-8-methylene-3-azabicyclo[3.3.1]non-2-en-2-
yl 1H-indol-3-yl ketone ˆ 8-Oxo-9-dehydromakomakine [21b]; (‡)-28). To a soln. of 149 mg (0.51 mmol) of
synthetic (‡)-makomakine ((‡)-18) in 7 ml of CHCl3 were added 5 ml of 1m aq. NaHCO3 and 165.5 mg
(0.65 mmol) of I2. After stirring at 238 for 3 h, Et3N (0.045 ml) was added. The mixture was stirred for an
additional 30 min at 238 and then poured onto 45 ml of aq. 1m Na2S2O3 and 6 ml of conc. aq. NH3 soln. Extraction
with 90 ml of CHCl3 (3Â), followed by drying the combined org. extracts (K2CO3) and evaporation led to a
orange crude product, which was purified by chromatography (silica gel, CHCl3/THF/Et3N 100 :20 :5): 75 mg
(50%) of (‡)-28. Slightly yellow powder, which was crystallized from Et2O. This product was identical in every
respect with a compound synthesized earlier via a different route [14].
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¬
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Received June 3, 2002