Proline-catalyzed asymmetric synthesis of syn - And anti -1,3-diamines

Article abstract of DOI:10.1021/jo401722e

A general organocatalytic strategy for asymmetric synthesis of both syn/anti-1,3-diamines has been developed. The strategy employs proline-catalyzed sequential α-amination and Horner-Wadsworth-Emmons (HWE) olefination of aldehydes as the key step where sy

Full text of DOI:10.1021/jo401722e

Article
pubs.acs.org/joc
Proline-Catalyzed Asymmetric Synthesis of syn- and anti-1,3-
Diamines
Pradeep Kumar,*,† Vishwajeet Jha,† and Rajesh Gonnade‡
†Organic Chemistry Division, CSIR-National Chemical Laboratory (CSIR-NCL), Homi Bhabha Road, Pune 411008, Maharashtra,
India
‡Centre for Material Characterization Division, CSIR-National Chemical Laboratory (CSIR-NCL), Homi Bhabha Road, Pune
411008, Maharashtra, India
S
* Supporting Information
ABSTRACT: A general organocatalytic strategy for asymmetric synthesis of both syn/anti-1,3-diamines has been developed.
The strategy employs proline-catalyzed sequential α-amination and Horner−Wadsworth−Emmons (HWE) olefination of
aldehydes as the key step where syn-1,3-diamine was obtained as the most favorable product.
polyols and 1,3-aminoalcohol, we were able to get good
selectivity for anti isomer as compared to syn isomer, wherein
steric factors interfere in the catalyst control to give lower level
of selectivity. Given the importance of 1,3-diamines, it would be
worthwhile to develop short reaction sequence for enantiose-
lective and diastereoselective synthesis of 1,3-diamines.
INTRODUCTION
■
The 1,3-diamine functionality with syn- or anti-configuration
are ubiquitous structural features in a wide range of natural
products and various bioactive compounds,1 viz., marine
alkaloids batzelladines,2 α-adrenoreceptor blockers manzaci-
din,3 antibiotic glycocinnamoylspermidines,4 or HIV-1 protease
inhibitors, such as A-74704.5 Additionally, 1,3-diamines have
also been used as ligands for asymmetric catalysis and chiral
core of numerous synthetic reagents.6
Increasingly, synthetic organic chemists are merging discrete
organic reactions in one-pot (referred to by various names, viz.,
domino reactions, sequential addition reactions, one-pot
multicomponent reactions, multicatalysis)7 to generate complex
organic molecules from simple starting material in order to
increase efficiencies and reduce the environmental impact in
terms of reduction in byproducts.8
Recently we and others have developed one-pot sequential
addition reaction sequence to synthesize γ-hydroxy esters,9a,10a
γ-amino-α,β-unsaturated ester10b from proline-catalyzed α-
amination,11a−d α-aminoxylation11e,f of aldehydes. We have
further used these reactions in a iterative or sequential manner
to develop synthetic protocols for syn/anti-1,3-polyols9a,b and
syn/anti-1,3-amino alcohols9c in good to useful level of
stereoinduction. Herein we wish to report the method for the
syntheses of syn- and anti-1,3-diamines. In case of both 1,3-
Despite the biological and pharmacological importance of
1,3-diamine, only few methods are reported in literature for
their stereoselective synthesis.12,13 The most widely used
strategy for their synthesis includes reduction of diimines,13b
pyrazolidines,13c,d pyrimidines,13e azides,13f quaternary immo-
nium salts generated in situ by aminoalkylation of enamines13g
or β-amino imines.13i Recently Trost et al. have reported
sequential process, which involves an asymmetric allylic
amination and subsequent formation and opening of amino
aziridines,13h while Menche et al. have reported stereodivergent
cyclization of urea-type substrates by intramolecular allylic
substitution.13j However, these methods involve specially
modified starting materials such as pyrimidines, diimines, and
amino imines being catalyzed by toxic metal catalysts like
Pd(PPh3)4, Pd2(dba)3, and Rh2(esp)2, etc.
Received: August 13, 2013
© XXXX American Chemical Society
A
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Scheme 3, the DMP oxidation of alcohol 6a furnished the
corresponding aldehyde, which was subsequently subjected to
α-amination using dibenzylazodicarboxylate (DBAD) and L-
proline as a catalyst to furnish α-aminoaldehyde, which on
further reduction with NaBH4 afforded the syn-1,3-diamine 7a
in 68% yield and 99.9:0.1 diastereomeric ratio.15 Surprisingly,
when the same sequence of reaction was repeated using D-
proline as a catalyst, we got anti-1,3-diamine 8a in 64% yield
and 3:1 diastereomeric ratio. The major anti-1,3-diamine
diastereomer was easily separated by flash silica gel column
chromatography. By analyzing the diastereomeric ratio of both
syn as well as anti product, we concluded that not only the
catalyst but also the existing stereochemistry of the substrate
play a major role in asymmetric induction of new chiral center
and favor the formation of syn product. To further prove this
hypothesis, we repeated the same sequence of reaction using
DL-proline as a catalyst and got diastereomeric ratio 4:1 in favor
of syn isomer. Overall these results are in contrast with those
observed in the case of syn/anti-1,3-diol9a and syn/anti-1,3-
amino alcohols,9b where the asymmetric induction for the anti-
isomer was found to be higher as compared to the syn-isomer.
However, a detailed literature survey revealed the observed
selectivity for the N−N−Cbz group,10b,16 as reported by
Sudalai et al. for the synthesis of syn-aminodiol.
RESULTS AND DISCUSSION
■
As a part of our ongoing research program aimed at developing
new organocatalytic protocols and their subsequent application
to asymmetric synthesis of biologically active natural products,9
we envisioned that the proline-catalyzed α-amination11a,b could
provide an easy access to 1,3-diamines in stereocontrolled
manner. However, it would be interesting to see the catalyst as
well as substrate role in determining the ratio of syn/anti-1,3-
diamine, since in this case we have bulky protected amine in
place of relatively smaller OTBS group as used in the previous
two cases. Our synthetic strategy for 1,3-diamines is illustrated
in Scheme 1.
Scheme 1. General Synthetic Strategy for 1,3-Diamines
The reaction sequence shows a wide substrate scope and is
compatible to different functionalities such as alkyl, substituted
alkyl, aryl, and substituted aryl groups. Excellent diastereomeric
ratio (dr ∼98:2 to ∼100) and good yields (62−68%) were
obtained for all the substrates in case of syn product, whereas
moderate to low diastereomeric ratio (dr 3:1 to 2:3) and good
yields (60−64%) were obtained for all the substrates in case of
anti product (Scheme 3).
In order to demonstrate the synthetic utility of this protocol,
we have accomplished a short synthesis of both diastereomers
of N-protected N2,N4-dimethylpentane-2,4-diamine 13 and 14.
The chiral diamine ligand forms a complex with Pt, which
interacts stereospecifically with DNA and even with mono-
nucleotides and acts as antitumor.17As illustrated in Scheme 4,
the diastereomerically pure syn-diamine 7e was subjected to
synthetic manipulation in order to achieve the synthesis of
target compound 13.
Toward this end, the free alcohol of protected syn-diamine 7e
was tosylated followed by treatment with LiAlH4 to furnish
compound 9. The N−N bond of compound 9 was cleaved with
Raney Ni under hydrogenation conditions, and free amine was
protected as its Boc derivative 11. Methylation of Boc
derivative gave the target compound 13. Same set of reactions
were repeated with 1,3-anti-diamine 8e to obtain the other
diastereomer 14.
In conclusion, a new, efficient, and organocatalytic strategy
has been developed for the stereocontrolled synthesis of both
syn- and anti-1,3-diamine using sequential α-amination and
HWE olefination reaction of an aldehyde as key step.
Interestingly, the syn-isomer was obtained as the most favorable
product. The synthetic application of this protocol was
demonstrated by the asymmetric synthesis of both the
diastereomers of N-protected N2,N4-dimethylpentane-2,4-dia-
mine.
Toward the synthesis of 1,3-diamine, we first proceed with
the synthesis of various protected γ-amino esters. Thus,
commercially available aldehydes 1a−f were subjected to
sequential α-amination using commercially available dibenzyla-
zodicarboxylate (DBAD) as the nitrogen source, L-proline as
catalyst, and subsequent Horner−Wadsworth−Emmons
(HWE) olefination using triethylphosphonoacetate to furnish
the γ-amino-α,β-unsaturated esters 2a−f in good yields (80−
87%) and excellent enantioselectivities (91−95%) and E/Z
ratio 98:2 (Table 1).
With protected γ-amino-α,β-unsaturated esters 2a−f in hand,
our next target was selective reduction of double bond in
presence of Cbz group. For this purpose, ester 2a was subjected
to hydrogenation conditions using different catalyst such as Pd/
C, PtO2, Pt, Lindlar’s catalyst, etc., but the formation of reduced
product 3 could not be observed (Scheme 2).
The unsaturated ester 2a was subjected to Mg/MeOH
condition,14 but interestingly we could obtain 4 as the only
product. Extension of conjugation may be the possible cause for
the formation of 4, as the same reaction when repeated with
acyclic substrate 2c did not afford the product 5; instead, the
starting material was recovered back (Scheme 2).
We resorted next to reduce the ester group. For this purpose,
ester 2a was treated with LiBH4 in THF, but to our surprise,
the double bond also got reduced with concomitant reduction
of the ester group to give alcohol 6a. As shown in the Table 2,
probably the reaction proceeds first via reduction of double
bond followed by reduction of ester group. To assess the
generality of this procedure for reduction of ester group as well
as double bond, various γ-amino-α,β-unsaturated esters 2a−f
were subjected to reduction conditions using LiBH4, and
similar results were obtained in all the cases (Table 2).
With substantial amount of various hydrazine alcohols 6a−f
in hand, our next aim was to introduce another amine
functionality stereoselectively at the 3-position. As depicted in
EXPERIMENTAL SECTION
■
General Information. All reactions requiring anhydrous con-
ditions were performed under a positive pressure of argon using oven-
dried glassware (110 °C), which was cooled under argon. Anhydrous
B
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Table 1. Synthesis of γ-Amino-α,β-unsaturated Esters
a
ee was determined by HPLC analysis.
on Orbitrap (quadrupole plus ion trap) and TOF mass analyzer. All
HPLC analyses used to determine enantiomeric purity were calibrated
with sample of the racemate.
Scheme 2. Attempted Reduction of Double Bond by
Hydrogenation Conditions
The physical and spectroscopic data of compounds 2a−e and 2f are
in accord with those described in literature.10b,9d
(R,E)-Dibenzyl 1-(5-ethoxy-5-oxo-1-phenylpent-3-en-2-yl)-
hydrazine-1,2-dicarboxylate (2a). [α]2D5 +8.44 (c 1.0, CHCl3)
{Lit10b {[α]D25 +8.5 (c 1.0, CHCl3)}. HPLC: Chiralcel OD-H (250 ×
4.6 mm) (2-propanol:petroleum ether = 3:97, flow rate 1.0 mL/min (λ
= 254 nm). Retention time (min): 67.692 (major) and 75.817
(minor). The racemic standard was prepared in the same way using
DL-proline as a catalyst. ee 95%
(R,E)-Dibenzyl 1-(5-ethoxy-1-(4-methoxyphenyl)-5-oxopent-
3-en-2-yl)hydrazine-1,2-dicarboxylate (2b). [α]2D5 +4.12 (c 1.0,
CHCl3) {Lit10b {[α]D25 +4.0 (c 1.0, CHCl3)}. HPLC: Kromasil 5−
Amycoat (250 × 4.6 mm) (2-propanol:petroleum ether = 10:90, flow
rate 0.7 mL/min (λ = 254 nm). Retention time (min): 57.192 (major)
and 63.683 (minor). The racemic standard was prepared in the same
way using DL-proline as a catalyst. ee 91%
(R,E)-Dibenzyl 1-(1-ethoxy-1-oxohept-2-en-4-yl)hydrazine-
1,2-dicarboxylate (2c). [α]2D5 +8.14 (c 1.0, CHCl3) {Lit10b {[α]2D5
+8.0 (c 1.0, CHCl3)}. HPLC: Kromasil 5−Amycoat (250 × 4.6 mm)
(2-propanol:petroleum ether = 10:90, flow rate 0.5 mL/min (λ = 254
nm). Retention time (min): 26.100 (major) and 36.575 (minor). The
racemic standard was prepared in the same way using DL-proline as a
catalyst. ee 94%
solvents were used for reactions. Solvents used for chromatography
were distilled at respective boiling points using known procedures.
Commercially available starting materials and reagents were used.
1
The IR spectra were recorded on FT-IR spectrometer. H NMR
spectra were recorded using deuterated solvent. Chemical shifts are
reported in ppm. Proton coupling constants (J) are reported as
absolute values in Hz and multiplicity (br, broadened; s, singlet; d,
douplet; t, triplet; m, multiplet). 13C NMR chemical shifts are reported
in ppm relative to the central line of CDCl3 (δ 77.0). Mass spectra
were taken on MS-TOF mass spectrometer. HRMS (ESI) were taken
(R,E)-Dibenzyl 1-(6-ethoxy-2-methyl-6-oxohex-4-en-3-yl)-
hydrazine-1,2-dicarboxylate (2d). ([α]2D5 +1.90 (c 1.0, CHCl3)
{Lit10b {[α]D25 +2.0 (c 1.0, CHCl3)}. HPLC: Kromasil 5−Amycoat
C
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Table 2. Reduction of Ester Group
(250 × 4.6 mm) (2-propanol:petroleum ether = 10:90, flow rate 0.7
mL/min (λ = 254 nm). Retention time (min): 19.250 (major) and
28.650 (minor). The racemic standard was prepared in the same way
using DL-proline as a catalyst. ee 92%
(R,E)-Dibenzyl 1-(5-ethoxy-5-oxopent-3-en-2-yl)hydrazine-
1,2-dicarboxylate (2e). [α]2D5 +5.09 (c 1.0, CHCl3) {Lit10b {[α]2D5
+5.0 (c 1.0, CHCl3)}. HPLC: Chiralcel OD-H (250 × 4.6 mm) (2-
propanol: n-hexane = 6:94, flow rate 1.0 mL/min (λ = 254 nm).
Retention time (min): 27.042 (minor) and 34.208 (major). The
racemic standard was prepared in the same way using DL-proline as a
catalyst. ee 93%
Dibenzyl (R,E)-1-(8-((tert-butyldimethylsilyl)oxy)-1-ethoxy-
1-oxooct-2-en-4-yl)hydrazine-1,2-dicarboxylate (2f). [α]D25
+2.69 (c 1.0, CHCl3) {Lit9d {[α]D25 +2.67 (c 1.0, CHCl3)}. HPLC:
Kromasil 5−Amycoat (250 × 4.6 mm) (2-propanol:petroleum ether =
10:90, flow rate 0.5 mL/min (λ = 230 nm). Retention time (min):
13.300 (major) and 16.225 (minor). The racemic standard was
prepared in the same way using DL-proline as a catalyst. ee 91%
Dibenzyl 1-((1Z,3E)-5-ethoxy-5-oxo-1-phenylpenta-1,3-
dien-2-yl)hydrazine-1,2-dicarboxylate 4. To a solution of
activated Mg (0.02 g, 0.8 mmol) under argon in dry MeOH (5 mL)
was added ethyl ester 2a (0.1 g, 0.2 mmol). The reaction mixture was
stirred for 3 h at 10 °C in an ice bath. The reaction mixture was
poured into 10 mL of ice-cooled 1 N HCl solution. The reaction
mixture was then treated with 1 N ammonium hydroxide solution to
adjust pH to 8 and extracted with ethyl acetate (3 × 5 mL). The
combined organic layers were washed with brine, dried over anhydrous
Na2SO4, and concentrated under reduced pressure to give crude
product. Silica gel column chromatography (petroleum ether:ethyl
acetate = 9:1) of the crude product gave dibenzyl 1-((1Z,3E)-5-
ethoxy-5-oxo-1-phenylpenta-1,3-dien-2-yl)hydrazine-1,2-dicarboxylate
4 as a colorless solid (0.08 g, 80%): mp 88 °C; IR (CHCl3, cm−1) νmax
3294, 3030, 1715, 1497, 1218; 1H NMR (200 MHz, CDCl3) δ 1.26 (t,
J = 7.1 Hz, 3H), 4.18 (q, J = 7.1 Hz, 2H), 5.14−5.24 (m, 4H), 6.07 (d,
J = 15.8 Hz, 1H), 7.25−7.36 (m, 17H), 7.61 (d, J = 15.5 Hz, 1H) ppm;
13C NMR (50 MHz, CDCl3) δ 14.2, 60.6, 6.9, 68.5, 120.8, 127.7,
128.2, 128.4, 128.5, 128.9, 129.7, 134.1, 135.3, 135.5, 136.2, 137.1,
138.6, 155.3, 156.1, 166.7 ppm; MS (ESI) m/z 523.18 (M + Na)+;
HRMS (ESI) m/z [M + H]+ Calcd for C29H29N2O6 501.2020, found
501.2019; [M + NH4]+ Calcd for C29H32N3O6 518.2286, found
518.2287.
(S)-Dibenzyl 1-(5-hydroxy-1-phenylpentan-2-yl)hydrazine-
1,2-dicarboxylate (6a). To a solution of ethyl ester 2a (0.1 g, 0.2
mmol) in THF (2 mL), was added LiBH4 (0.01 g, 0.6 mmol) at 0 °C.
The reaction mixture was stirred at rt for 2 h. It was then quenched
with aqueous ammonium chloride solution (1 mL) and extracted with
ethyl acetate (3 × 5 mL). The combined organic layers were washed
with brine, dried over anhydrous Na2SO4, and concentrated under
reduced pressure to give crude product. Silica gel column
chromatography (petroleum ether:ethyl acetate = 7:3) of the crude
product gave 6a as a colorless solid (0.09 g, 92%): mp 97 °C; [α]D25
+13.08 (c 1.1, CHCl3); IR (CHCl3, cm−1) νmax 3446, 3285, 2927,
1
1709, 1454, 1221, 1057; H NMR (200 MHz, CDCl3) δ 1.45−1.58
(m, 2H), 1.71−1.76 (m, 2H), 2.72−2.86 (m, 2H), 3.26 (brs, 1H),
D
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Scheme 3. Synthesis of syn/anti-1,3-Diamine
Scheme 4. Synthesis of N2,N4-Dimethylpentane-2,4-diamine
3.49−3.73 (m, 2H), 4.37−4.63 (m, 1H), 5.05−5.18 (m, 4H), 6.34 (s,
1H), 7.12−7.22 (m, 5H), 7.29−7.44 (m, 10H) ppm; 13C NMR (50
MHz, CDCl3) δ 27.5, 28.9, 38.8, 60.3, 61.7, 67.3, 67.8, 126.0, 127.1,
127.8, 128.2, 128.6, 136.3, 135.7, 138.2, 155.8, 156.7 ppm; MS (ESI)
m/z 485.19 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd for
C27H31O5N2 463.2227, found 463.2226; [M + Na]+ Calcd for
C27H30N2O5Na 485.2044, found 485.2044
(S)-Dibenzyl 1-(5-hydroxy-1-(4-methoxyphenyl)pentan-2-
yl)hydrazine-1,2-dicarboxylate (6b). Colorless solid (0.085 g,
92%): mp 120 °C; [α]D25 +20.08 (c 0.75, CHCl3); IR (CHCl3, cm−1)
1
νmax 3420, 2925, 1711, 1456, 1127; H NMR (200 MHz, CDCl3) δ
1.39−1.54 (m, 2H), 1.69−1.93 (m, 2H), 2.62−2.84 (m, 2H), 3.48−
3.73 (m, 2H), 3.76 (s, 3H), 4.29−4.62 (m, 1H), 5.00−5.18 (m, 4H),
6.25 (brs, 1H), 6.78 (d, J = 8.5 Hz, 2H), 6.98−7.16 (m, 3H), 7.27−
7.42 (m, 9H) ppm; 13C NMR (50 MHz, CDCl3) δ 27.9, 29.4, 38.1,
55.1, 60.5, 62.2, 67.8, 68.2, 113.9, 127.4, 127.9, 128.2, 128.4, 128.5,
129.6, 129.8, 130.1, 135.4, 135.7, 135.9, 155.9, 156.9, 158.1 ppm; MS
(ESI) m/z 515.21 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd for
C28H33N2O6 493.2333, found 493.2335; [M + Na]+ Calcd for
C28H32N2O6Na 515.2153, found 515.2155
E
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(R)-Dibenzyl 1-(1-hydroxyheptan-4-yl)hydrazine-1,2-dicar-
boxylate (6c). Colorless solid (0.081 g, 89%): mp 95 °C; [α]D25
+4.14 (c 1.8, CHCl3); IR (CHCl3, cm−1) νmax 3461, 3274, 2961, 1711,
CDCl3) δ 1.41−1.70 (m, 1H), 1.75−2.12 (m, 1H), 2.72−3.14 (m,
2H), 3.39−3.61 (m, 2H), 3.66−3.93 (m, 1H), 4.23−4.52 (m, 1H),
4.85−5.35 (m, 8H), 6.19−6.33 (m, 1H), 7.12−7.44 (m, 25H), 7.94−
8.16 (m, 1H) ppm; 13C NMR (100 MHz, CDCl3) δ 29.6, 37.7, 57.9,
61.7, 61.8, 67.9, 68.2, 68.4, 68.6, 126.6, 127.2, 127.5, 127.8, 128.0,
128.4, 128., 128.7, 135.1, 135.5, 156.7, 156.8, 158.6, 159.0 ppm; MS
(ESI) m/z 783.33 (M + Na)+, 799.30 (M + K)+; HRMS (ESI) m/z
[M + H]+ Calcd for C43H45N4O9 761.3181, found 761.3182.
Diastereomeric ratio was determined by HPLC analysis; 99.9:0.1 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.4 mL/min. IPA:petroleum ether = 6:4; tR for
(anti)-isomer = 25.800 min and tR for (syn)-isomer = 19.667 min.
Using the same procedure as described for synthesis of 7a,
compounds 7b−7f were prepared.
1
1692, 1457, 1042; H NMR (200 MHz, CDCl3) δ 0.89 (m, 3H),
1.10−1.56 (m, 8H), 3.30−3.61 (m, 2H), 4.06−4.23 (m, 1H), 5.04−
5.24 (m, 4H), 6.47 (brs, 1H), 7.26−7.43 (m, 10H) ppm; 13C NMR
(50 MHz, CDCl3) δ 13.8, 19.6, 28.6, 29.3, 34.7, 57.8, 62.3, 67.8, 68.2,
127.6, 127.8, 128.0, 128.2, 128.4, 128.5, 135.5, 135.8, 135.9, 156.3,
156.9 ppm; MS (ESI) m/z 437.12 (M + Na)+; HRMS (ESI) m/z [M
+ H]+ Calcd for C23H31N2O5 415.2227, found 415.2224; [M + Na]+
Calcd for C23H30N2O5Na 437.2047, found 437.2042.
(S)-Dibenzyl 1-(6-hydroxy-2-methylhexan-3-yl)hydrazine-
1,2-dicarboxylate (6d). Colorless solid (0.080 g, 88%): mp 97 °C;
[α]D25 +0.96 (c 0.9, CHCl3); IR (CHCl3, cm−1) νmax 3284, 2960, 1711,
1657, 1410, 1049; 1H NMR (200 MHz, CDCl3) δ 0.83−0.97 (m, 6H),
1.52−1.80 (m, 5H), 3.26−3.69 (m, 2H), 3.87−4.12 (m, 1H), 5.10−
5.19 (m, 4H), 6.49 (brs, 1H), 7.26−7.35 (m, 10H) ppm; 13C NMR
(50 MHz, CDCl3) δ 19.7, 20.2, 25.2, 29.4, 30.4, 62.1, 64.1, 67.6, 68.2,
127.5, 127.7, 127.9, 128.1, 128.4, 135.5, 135.8, 135.9, 156.5, 157.2
ppm; MS (ESI) m/z 437.12 (M + Na)+; HRMS (ESI) m/z [M + H]+
Calcd for C23H31N2O5 415.2227, found 415.2224; [M + Na]+ Calcd
for C23H30N2O5Na 437.2047, found 437.2042.
(R)-Dibenzyl 1-(5-hydroxypentan-2-yl)hydrazine-1,2-dicar-
boxylate (6e). Colorless solid (0.081 g, 89%): mp 81 °C; [α]D25
−2.75 (c 1.0, CHCl3); IR (CHCl3, cm−1) νmax 3292, 2941, 1711, 1658,
1455, 1221; 1H NMR (200 MHz, CDCl3) δ 1.16 (d, J = 6.5 Hz, 3H),
1.37−1.50 (m, 2H), 1.63−1.73 (m, 2H), 3.51−3.73 (m, 2H), 4.21−
4.44 (m, 1H), 5.08−5.21 (m, 4H), 6.49 (brs, 1H), 7.27−7.36 (m,
10H) ppm; 13C NMR (50 MHz, CDCl3) δ 17.9, 29.1, 29.9, 53.5, 62.0,
67.5, 67.8, 127.6, 127.9, 128.2, 128.4, 135.6, 135.8, 155.8, 156.9 ppm;
MS (ESI) m/z 409.14 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd
for C21H27N2O5 387.1914, found 387.1913; [M + Na]+ Calcd for
C21H26N2O5Na 409.1734, found 409.1732.
1,1′-((2R,4R)-Tetrabenzyl 1-hydroxy-5-(4-methoxyphenyl)-
pentane-2,4-diyl)bis(hydrazine-1,2-dicarboxylate) (7b). Waxy
solid (0.104 g, 65%): [α]2D5 +12.08 (c 1.1, CHCl3); IR (CHCl3,
1
cm−1) νmax 3294, 2927, 1718, 1512, 1455, 1247, 1059; H NMR (200
MHz, CDCl3) δ 1.45−1.74 (m, 2H), 2.61−2.88 (m, 2H), 3.33−3.70
(m, 3H), 3.77 (s, 3H), 4.15−4.69 (m, 2H), 4.88−5.37 (m, 8H), 6.21−
6.49 (m, 1H), 6.73−6.82 (m, 2H), 7.00−7.09 (m, 2H), 7.19−7.48 (m,
20H), 8.03−8.21 (m, 1H) ppm; 13C NMR (100 MHz, CDCl3) δ 29.6,
38.1, 55.0, 60.3, 61.6, 62.2, 67.6, 67.9, 68.2, 68.5, 113.9, 114.0, 127.1,
127.4, 127.9, 128.2, 128.3, 128.5, 129.5, 129.6, 129.9, 135.1, 135.4,
135.7, 135.9, 155.9, 156.4, 156.8, 157.3, 158.1 ppm; MS (ESI) m/z
813.37 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd for
C44H47N4O10 791.3287, found 791.3288; [M + Na]+ Calcd for
C44H46N4O10Na 813.3106, found 813.3095.
Diastereomeric ratio was determined by HPLC analysis; 99.9:0.1 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 37.550 min and tR for (syn)-isomer = 29.225 min.
1,1′-((2R,4R)-Tetrabenzyl 1-hydroxyheptane-2,4-diyl)bis-
(hydrazine-1,2-dicarboxylate) (7c). Waxy solid (0.107 g, 62%):
[α]2D5 −5.32 (c 1.85, CHCl3); IR (CHCl3, cm−1) νmax 3293, 2925,
(R)-Dibenzyl 1-(8-((tert-butyldimethylsilyl)oxy)-1-hydrox-
yoctan-4-yl)hydrazine-1,2-dicarboxylate (6f). Waxy solid (0.084
g, 90%): [α]2D5 +11.51 (c 1.0, CHCl3); IR (CHCl3, cm−1) νmax 3294,
1
1714, 1498, 1456, 1259, 1049; H NMR (200 MHz, CDCl3) δ 0.72−
1
295, 1705, 1658, 1224; H NMR (200 MHz, CDCl3) δ 0.00 (s, 6H),
0.88 (m, 3H), 1.26−1.34 (m, 3H), 1.48−1.80 (m, 3H), 3.40−3.72 (m,
2H), 3.88−4.02 (m, 1H), 4.21−4.54 (m, 2H), 4.83−5.33 (m, 8H),
6.64−6.96 (m, 1H), 7.22−7.48 (m, 20H), 7.56−7.83 (m, 1H) ppm;
13C NMR (125 MHz, CDCl3) δ 13.5, 19.5, 31.6, 34.7, 57.7, 61.6, 62.0,
0.85 (s, 9H), 1.16−1.73 (m, 10H), 2.48 (brs, 1H), 3.27−3.55 (m, 4H),
3.90−4.26 (m, 1H), 4.85−5.20 (m, 4H), 7.11−7.42 (m, 10H) ppm;
13C NMR (50 MHz, CDCl3) δ −5.5, 18.1, 21.9, 22.2, 25.7, 28.4, 28.9,
32.1, 57.9, 61.8, 62.6, 67.3, 67.5, 127.3, 127.8, 127.9, 128.2, 135.5,
135.9, 156.2, 156.7 ppm; MS (ESI) m/z 581.24 (M + Na)+; HRMS
(ESI) m/z [M + H]+ Calcd for C30H47N2O6Si 559.3198, found
559.3189; [M + Na]+ Calcd for C30H46N2O6NaSi 581.3017, found
581.3010.
67.5, 67.8, 68.1, 68.4, 127.2, 127.4, 127.7, 127.9, 128.1, 128.3, 128.4,
129.8, 132.9, 135.4, 135.5, 135.8, 156.2, 156.5, 156.7, 156.9 ppm; MS
(ESI) m/z 735.34 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd for
C39H45N4O9 713.3181, found 713.3182; [M + Na]+ Calcd for
C39H44N4O9Na 735.3001, found 735.2983.
1,1′-((2R,4R)-Tetrabenzyl 1-hydroxy-5-phenylpentane-2,4-
diyl)bis(hydrazine-1,2-dicarboxylate) (7a). To a solution of
alcohol 6a (0.1g, 0.216 mmol) in DCM (2 mL) was added DMP
(0.137g, 3.25 mmol) at 0 °C. The reaction mixture was stirred at rt for
1 h. It was then quenched with a 1:1 mixture of (10%) aqueous
Na2S2O3 solution and saturated NaHCO3 solution and extracted with
diethyl ether (3 × 5 mL). The combined organic layers were washed
with brine, dried over anhydrous Na2SO4, and concentrated under
reduced pressure to give aldehyde as a colorless liquid, which was
directly used in the next step without further purification.
To a cooled solution of dibenzyl azodicarboxylate (DBAD) (0.065
g, 0.216 mmol) and L-proline (0.003 g, 10 mol %) in CH3CN (2 mL)
at 0 °C was added the above aldehyde (0.1 g, 0.216 mmol), and the
mixture was stirred for 4 h at 0 °C and further for 1 h at 10 °C. Then
the reaction mixture was cooled to 0 °C, treated with ethanol 1 mL
and NaBH4 (0.02 g), and stirred for 5 min at 0 °C. It was then
quenched with aqueous ammonium chloride solution (3 mL) and
extracted with ethyl acetate (3 × 5 mL). The combined organic layers
were washed with brine, dried over anhydrous Na2SO4, and
concentrated under reduced pressure to give crude product. Silica
gel column chromatography (petroleum ether:ethyl acetate = 70:30)
of the crude product gave 1,1′-((2R,4R)- tetrabenzyl 1-hydroxy-5-
phenylpentane-2,4-diyl)bis(hydrazine-1,2-dicarboxylate) 7a as a waxy
solid (0.112 g, yield 68%): [α]2D5 +37.41 (c 1.05, CHCl3); IR (CHCl3,
cm−1) νmax 3292, 2925, 1718, 1455, 1219, 1060; 1H NMR (200 MHz,
Diastereomeric ratio was determined by HPLC analysis; 99:1 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 22.283 min and tR for (syn)-isomer = 14.792 min.
1,1′-((2R,4S)-Tetrabenzyl 1-hydroxy-5-methylhexane-2,4-
diyl)bis(hydrazine-1,2-dicarboxylate) (7d). Waxy solid (0.110 g,
64%): [α]2D5 −8.29 (c 1.0, CHCl3); IR (CHCl3, cm−1) νmax 3280, 2960,
1
1715, 1498, 1456, 1260, 1051; H NMR (200 MHz, CDCl3) δ 0.83−
0.94 (m, 6H), 1.55−1.84 (m, 3H), 3.42−3.66 (m, 2H), 3.75−4.16 (m,
3H), 5.08−5.14 (m, 8H), 5.65−5.78 (m, 1H), 6.72−6.91 (m, 1H),
7.26−7.39 (m, 20H) ppm; 13C NMR (125 MHz, CDCl3) δ 19.6, 19.7,
29.4, 30.4, 61.4, 62.5, 64.2, 67.6, 67.9, 68.3, 127.2, 127.5, 127.7, 127.9,
128.0, 128.3, 128.4, 129.9, 130.7, 131.9, 135.5, 135.8, 156.5, 156.7,
157.2 ppm; MS (ESI) m/z 735.34 (M + Na)+; HRMS (ESI) m/z [M
+ H]+ Calcd for C39H45N4O9 713.3181, found 713.3182; [M + Na]+
Calcd for C39H44N4O9Na 735.3001, found 735.2983.
Diastereomeric ratio was determined by HPLC analysis; 97.5:2.5 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 25.542 min and tR for (syn)-isomer = 17.342 min.
1,1′-((2R,4R)-Tetrabenzyl 1-hydroxypentane-2,4-diyl)bis-
(hydrazine-1,2-dicarboxylate) (7e). Waxy solid (0.115 g, 65%):
[α]2D5 −10.17 (c 1.0, CHCl3); IR (CHCl3, cm−1) νmax 3290, 2936,
1
1712, 1498, 1455, 1223, 1050; H NMR (200 MHz, CDCl3) δ 1.08−
1.23 (m, 3H), 1.28−1.53 (m, 2H), 3.30−3.66 (m, 3H), 4.02−4.47 (m,
F
dx.doi.org/10.1021/jo401722e | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
2H), 4.91−5.53 (m, 8H), 6.84−6.98 (m, 1H), 7.19−7.41 (m, 20H),
7.64−7.75 (m, 1H) ppm; 13C NMR (125 MHz, CDCl3) δ 22.6, 29.6,
61.8, 61.9, 62.3, 67.7, 67.9, 68.1, 68.5, 127.4, 127.7, 127.8, 127.9, 128.1,
128.4, 128.5, 135.3, 135.5, 156.4, 156.6, 156.7, 156.8 ppm; MS (ESI)
m/z 707.40 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd for
C37H41N4O9 685.2868, found 685.2869; [M + Na]+ Calcd for
C37H40N4O9Na 707.2687, found 707.2675.
Diastereomeric ratio was determined by HPLC analysis; 99.7:0.3 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 26.558 min and tR for (syn)-isomer = 22.017 min.
1,1′-((2R,4R)-Tetrabenzyl 8-((tert-butyldimethylsilyl)oxy)-1-
hydroxyoctane-2,4-diyl)bis(hydrazine-1,2-dicarboxylate) (7f).
Waxy solid (0.117 g, 63%): [α]2D5 +4.45 (c 1.4, CHCl3); IR (CHCl3,
cm−1) νmax 3295, 2932, 1712, 1496, 1261, 1051; 1H NMR (500 MHz,
CDCl3) δ 0.05 (s, 6H), 0.93 (s, 9H), 1.31−1.89 (m, 8H), 3.46−3.73
(m, 4H), 3.83−4.61 (m, 3H), 4.83−5.39 (m, 8H), 6.88−6.99 (m, 1H),
7.12−7.34 (m, 20H), 7.91−8.28 (m, 1H) ppm; 13C NMR (125 MHz,
CDCl3) δ −5.4, 18.2, 22.6, 25.8, 29.5, 31.8, 61.6, 61.9, 62.7, 67.9, 68.1,
68.4, 127.2, 127.7, 127.9, 128.2, 128.4, 131.3, 132.4, 135.4, 141.3,
156.3, 156.7, 156.8 ppm; MS (ESI) m/z 879.24 (M + Na)+; HRMS
(ESI) m/z [M + Na]+ Calcd for C46H60N4O10NaSi 879.3971, found
879.3964.
MHz, CDCl3) δ 13.8, 19.6, 29.7, 34.8, 57.7, 58.8, 62.3, 67.8, 67.9, 68.1,
68.3, 126.9, 127.6, 127.7, 128.0, 128.2, 128.5, 135.5, 135.8, 135.9,
156.3, 156.6, 156.9, 157.2 ppm; MS (ESI) m/z 735.34 (M + Na)+;
HRMS (ESI) m/z [M + H]+ Calcd for C39H45N4O9 713.3181, found
713.3182; [M + Na]+ Calcd for C39H44N4O9Na 735.3001, found
735.2983.
Diastereomeric ratio was determined by HPLC analysis; 3:2 dr. UV
detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 22.533 min and tR for (syn)-isomer = 15.575 min.
1,1′-((2S,4S)-Tetrabenzyl 1-hydroxy-5-methylhexane-2,4-
diyl)bis(hydrazine-1,2-dicarboxylate) (8d). Waxy solid (0.110 g,
64%): [α]2D5 −10.14 (c 1.5, CHCl3); IR (CHCl3, cm−1) νmax 3280,
1
2960, 1715, 1498, 1456, 1260, 1051; H NMR (200 MHz, CDCl3) δ
0.83−0.95 (m, 6H), 1.47−1.84 (m, 3H), 3.34−3.93 (m, 4H), 4.05−
4.24 (m, 1H), 4.77−5.28 (m, 8H), 5.65−5.78 (m, 1H), 6.77−7.03 (m,
1H), 7.25−7.39 (m, 20H) ppm; 13C NMR (100 MHz, CDCl3) δ 19.6,
19.9, 29.4, 30.4, 62.3, 62.6, 64.2, 67.7, 67.8, 68.0, 68.3, 127.3, 127.5,
127.6, 127.7, 127.9, 128.1, 128.3, 128.4, 128.5, 129.9, 135.4, 135.8,
156.4, 156.7, 156.9, 157.2 ppm; MS (ESI) m/z 735.34 (M + Na)+;
HRMS (ESI) m/z [M + H]+ Calcd for C39H45N4O9 713.3181, found
713.3182; [M + Na]+ Calcd for C39H44N4O9Na 735.3001, found
735.2983.
Diastereomeric ratio was determined by HPLC analysis; 3:1 dr. UV
detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 24.817 min and tR for (syn)-isomer = 17.308 min.
1,1′-((2S,4R)-Tetrabenzyl 1-hydroxypentane-2,4-diyl)bis-
(hydrazine-1,2-dicarboxylate) (8e). Waxy solid (0.108 g, 61%):
[α]D25 −3.08 (c 2.6, CHCl3); IR (CHCl3, cm−1) νmax 3290, 2936, 1712,
Diastereomeric ratio was determined by HPLC analysis; 99:1 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 27.542 min and tR for (syn)-isomer = 23.642 min.
Using the same procedure as described for the synthesis of 7a and
using D-proline as a catalyst in α-amination step, compounds 8a−8f
were prepared.
1
1498, 1455, 1223, 1050; H NMR (200 MHz, CDCl3) δ 1.14 (d, J =
1,1′-((2S,4R)-Tetrabenzyl 1-hydroxy-5-phenylpentane-2,4-
diyl)bis(hydrazine-1,2-dicarboxylate) (8a). Waxy solid (0.105 g,
64%): [α]2D5 +2.74 (c 1.7, CHCl3); IR (CHCl3, cm−1) νmax 3292,, 2925,
6.4 Hz, 3H), 1.28−1.48 (m, 2H), 3.03−3.22 (s, 1H), 3.36−3.57 (m,
2H), 4.02−4.41 (m, 2H), 4.75−5.29 (m, 4H), 6.79−7.03 (m, 1H),
7.12−7.46 (m, 20H) ppm; 13C NMR (125 MHz, CDCl3) δ 17.9, 30.0,
53.5, 54.5, 62.2, 67.6, 67.8, 68.1, 127.3, 127.6, 128.0, 128.2, 135.6,
135.8, 155.7, 155.8, 156.6, 156.8 ppm; MS (ESI) m/z 707.40 (M +
Na)+; HRMS (ESI) m/z [M + H]+ Calcd for C37H41N4O9 685.2868,
found 685.2869; [M + Na]+ Calcd for C37H40N4O9Na 707.2687,
found 707.2675.
Diastereomeric ratio was determined by HPLC analysis; 57:43 dr.
UV detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 26.092 min and tR for (syn)-isomer = 21.625 min.
1,1′-((2S,4R)-Tetrabenzyl 8-((tert-butyldimethylsilyl)oxy)-1-
hydroxyoctane-2,4-diyl)bis(hydrazine-1,2-dicarboxylate) (8f).
Waxy solid (0.115 g, 62%): [α]2D5 −5.59 (c 1.2, CHCl3); IR (CHCl3,
cm−1) νmax 3295, 2932, 1712, 1496, 1261, 1051; 1H NMR (200 MHz,
CDCl3) δ 0.00 (s, 6H), 0.85 (s, 9H), 1.26−1.32 (m, 3H), 1.38−1.67
(m, 5H), 2.51 (brs, 1H), 3.40−4.27 (m, 6H), 4.79−5.34 (m, 8H),
6.79−6.97 (m, 1H), 7.27 (m, 20H) ppm; 13C NMR (50 MHz, CDCl3)
δ −5.4, 18.3, 22.2, 25.9, 29.6, 32.3, 62.2, 62.4, 62.7, 67.7, 67.9, 68.1,
127.5, 128.1, 128.2, 128.4, 128.5, 135.5, 135.7, 156.3, 156.5, 156.8
ppm; MS (ESI) m/z 879.24 (M + Na)+; HRMS (ESI) m/z [M + Na]+
Calcd for C46H60N4O10NaSi 879.3971, found 879.3964.
Diastereomeric ratio was determined by HPLC analysis; 5:3 dr. UV
detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 26.200 min and tR for (syn)-isomer = 21.050 min.
Di-tert-butyl ((2R,4S)-pentane-2,4-diyl)dicarbamate 11. The
solution of 1,1′-((2R,4R)-tetrabenzyl 1-hydroxypentane-2,4-diyl)bis-
(hydrazine-1,2-dicarboxylate 7e (0.5g, 0.73 mmol) in DCM was
treated with triethylamine (0.148g, 1.46 mmol), and TsCl (0.21g, 1.1
mmol) was added at 0 °C followed by addition of catalytic DMAP.
The reaction mixture was stirred at rt for 2 h. After completion of
reaction, the reaction mixture was quenched with addition of water
and extracted with DCM (3 × 15 mL). The combined organic layers
were washed with brine, dried over anhydrous Na2SO4, and
concentrated under reduced pressure to give crude tosyl compound.
This crude tosyl compound was then treated with LiAlH4 (0.03g, 0.8
mmol) in THF for 1 h. The reaction was quenched by addition of
1
1718, 1455, 1219, 1060; H NMR (200 MHz, CDCl3) δ 1.43−1.82
(m, 2H), 2.49−2.99 (m, 2H), 3.11−3.71 (m, 2H), 4.18−4.73 (m, 2H),
4.88−5.18 (m, 8H), 6.42−6.57 (m, 1H), 7.32 (m, 25H), 7.92−8.21
(m, 1H) ppm; 13C NMR (125 MHz, CDCl3) δ 29.1, 38.9, 52.6, 60.4,
61.9, 67.3, 67.5, 67.7, 67.9, 127.2, 127.7, 127.9, 128.3, 128.7, 128.8,
129.7, 132.8, 134.9, 135.4, 135.8, 138.2, 155.8, 156.3, 156.7, 157.2
ppm; MS (ESI) m/z 783.33 (M + Na)+; HRMS (ESI) m/z [M + H]+
Calcd for C43H45N4O9 761.3181, found 761.3182.
Diastereomeric ratio was determined by HPLC analysis; 3:1 dr. UV
detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.4 mL/min. IPA:petroleum ether = 6:4; tR for
(anti)-isomer = 22.825 min and tR for (syn)-isomer = 20.317 min.
1,1′-((2S,4R)-Tetrabenzyl 1-hydroxy-5-(4-methoxyphenyl)-
pentane-2,4-diyl)bis(hydrazine-1,2-dicarboxylate) (8b). Waxy
solid (0.100 g, 62%): [α]2D5 +13.24 (c 1.0, CHCl3); IR (CHCl3,
1
cm−1) νmax 3294, 2927, 1718, 1512, 1455, 1247, 1059; H NMR (200
MHz, CDCl3) δ 1.30−1.49 (m, 2H), 2.46−2.71 (m, 2H), 3.40−3.61
(m, 3H), 3.66 (s, 3H), 3.90−4.58 (m, 2H), 4.67−5.17 (m, 8H), 6.27−
6.43 (m, 1H), 6.69 (d, J = 7.8 Hz, 2H), 6.95 (d, J = 7.8 Hz, 2H), 7.02−
7.23 (m, 20H), 7.45−7.73 (m, 1H) ppm; 13C NMR (100 MHz,
CDCl3) δ 29.6, 38.1, 55.1, 60.4, 62.2, 62.3, 67.8, 67.9, 68.2, 113.9,
127.5, 127.9, 128.2, 128.4, 128.5, 129.4, 129.6, 129.8, 129.9, 135.2,
135.4, 135.7, 135.9, 155.9, 156.5, 156.8, 157.4, 158.1 ppm; MS (ESI)
m/z 813.37 (M + Na)+; HRMS (ESI) m/z [M + H]+ Calcd for
C44H47N4O10 791.3287, found 791.3288; [M + Na]+ Calcd for
C44H46N4O10Na 813.3106, found 813.3095.
Diastereomeric ratio was determined by HPLC analysis; 2:3 dr. UV
detector: Shimadzu Class-VP V6.12 SP5. Column: Kromasil 5−
AmyCoat. Flow rate: 0.5 mL/min. IPA:petroleum ether = 3:7; tR for
(anti)-isomer = 37.185 min and tR for (syn)-isomer = 31.017 min.
1,1′-((2S,4R)-Tetrabenzyl 1-hydroxyheptane-2,4-diyl)bis-
(hydrazine-1,2-dicarboxylate) (8c). Waxy solid (0.103 g, 60%):
[α]D25 −2.27 (c 1.0, CHCl3); IR (CHCl3, cm−1) νmax 3293, 2925, 1714,
1
1498, 1456, 1259, 1049; H NMR (200 MHz, CDCl3) δ 0.86−0.89
(m, 3H), 1.11−1.27 (m, 2H), 1.30−1.38 (m, 2H), 1.53−1.64 (m, 2H),
3.42−3.76 (m, 3H), 3.90−4.39 (m, 2H), 4.86−5.30 (m, 8H), 6.70 (m,
1H), 7.18−7.42 (m, 20H), 7.58−7.79 (m, 1H) ppm; 13C NMR (100
G
dx.doi.org/10.1021/jo401722e | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
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saturated Na2SO4 solution. The mixture was filtered with pad of Celite
and washed with EtOAc. The organic layer was washed with brine,
dried over anhydrous Na2SO4, and concentrated under reduced
pressure to give crude diamine product 9, which was directly used in
the next step without further purification.
boc derivative. Silica gel column chromatography (petroleum
ether:ethyl acetate = 80:20) of the crude product gave N,N′-
((2R,4R)-pentane-2,4-diyl)bis(4-methylbenzenesulfonamide) 15 as a
crystalline solid (0.148 g, 50%): mp 115 °C; IR (CHCl3, cm−1) νmax
1
3275, 2928, 1328, 1161; H NMR (200 MHz, CDCl3) δ 0.88 (d, J =
6.5 Hz, 6H), 1.39−1.50 (m, 1H), 1.69−1.79 (m, 1H), 2.42 (s, 6H),
3.21−3.47 (m, 2H), 4.46 (d, J = 8.6 Hz, 2H), 7.29 (d, J = 8.4 Hz, 4H),
7.74 (d, J = 8.4 Hz, 4H) ppm; 13C NMR (50 MHz, CDCl3) δ 21.4,
21.5, 45.7, 47.2, 127.0, 129.7, 137.9, 143.3 ppm; MS (ESI) m/z 433.04
(M + Na)+; HRMS (ESI) m/z [M + Na]+ Calcd for C19H26N2O4S2Na
433.1226, found 433.1224.
The solution of crude diamine product 9 in MeOH (10 mL) and
acetic acid (5 drops) was treated with Raney nickel (0.8 g, excess)
under H2 (80 psi) atmosphere for 24 h. The reaction mixture was then
filtered over Celite and concentrated to give crude free diamine, which
was further treated with triethylamine (0.3g, 2.92 mmol), (Boc)2O
(0.65 mL, 2.92 mmol) in dry DCM (2 mL) for 2 h. Ice pieces were
added to the reaction mixture, and organic layer was separated. The
aqueous layer was extracted with diethyl ether (3 × 5 mL). The
combined organic layers were washed with brine, dried (Na2SO4), and
concentrated under reduced pressure to give crude N-boc derivative.
Silica gel column chromatography (petroleum ether:ethyl acetate =
85:15) of the crude product gave 11 as a waxy solid (0.121 g, 51%): IR
N,N′-((2R,4R)-Pentane-2,4-diyl)bis(4-methylbenzenesulfona-
mide) (16). Crystalline solid (0.148 g, 50%): mp 113 °C; [α]2D5 +0.15
1
(c 0.75, CHCl3); IR (CHCl3, cm−1) νmax 3275, 2928, 1328, 1161; H
NMR (200 MHz, CDCl3) δ 0.96 (d, J = 6.7 Hz, 6H), 1.59−1.63 (m,
2H), 2.44 (s, 6H), 3.43−3.57 (m, 2H), 4.61 (d, J = 7.8 Hz, 2H), 7.32
(d, J = 8.3 Hz, 4H), 7.78 (d, J = 8.3 Hz, 4H) ppm; 13C NMR (50
MHz, CDCl3) δ 20.8, 21.5, 44.6, 47.4, 127.0, 129.7, 138.3, 143.3 ppm;
MS (ESI) m/z 433.04 (M + Na)+; HRMS (ESI) m/z [M + Na]+
Calcd for C19H26N2O4S2Na 433.1226, found 433.1224.
1
(CHCl3, cm−1) νmax 3363, 2976, 1690, 1523, 1170; H NMR (200
MHz, CDCl3) δ 1.14 (d, J = 6.4 Hz, 6H), 1.43 (s, 18H), 1.67 (m, 2H),
3.62−3.76 (m, 2H), 4.38−4.59 (brs, 2H) ppm; 13C NMR (50 MHz,
CDCl3) δ 21.1, 28.4, 29.7, 44.1, 79.1, 155.3 ppm; MS (ESI) m/z
325.15 (M + Na)+; HRMS (ESI) m/z [M + Na]+ Calcd for
C15H30N2O4Na 325.2096, found 325.2098.
Di-tert-butyl ((2R,4R)-pentane-2,4-diyl)dicarbamate (12).
Waxy solid (0.121 g, 51%): [α]2D5 +5.92 (c 1.0, CHCl3); IR (CHCl3,
cm−1) νmax 3363, 2976, 1690, 1523, 1170; 1H NMR (200 MHz,
CDCl3) δ 1.17 (d, J = 6.7 Hz, 6H), 1.44 (s, 18H), 1.53−1.55 (m, 2H),
3.62−3.76 (m, 2H), 4.41−4.52 (brs, 2H) ppm; 13C NMR (50 MHz,
CDCl3) δ 21.0, 28.4, 29.6, 43.9, 79.0, 156.2 ppm; MS (ESI) m/z
325.15 (M + Na)+; HRMS (ESI) m/z [M + Na]+ Calcd for
C15H30N2O4Na 325.2096, found 325.2098.
D i - t e r t - b u t y l ( ( 2 R , 4 S ) - p e n t a n e - 2 , 4 - d i y l ) b i s -
(methylcarbamate) (13). To a stirred solution of 11 (0.03 g,
0.116 mmol) in dry toluene (3 mL) was added NaH (0.010 g, 0.464
mmol), CH3I (0.1 mL, 1.55 mmol), and the reaction mixture was
heated at 85 °C for 5 h. The reaction mixture was then diluted with
EtOH (5 mL) and H2O (2 mL), and the organic phase was separated.
The aqueous layer was extracted with CH2Cl2 (3 × 4 mL). The
combined organic layers were washed with brine, dried (Na2SO4), and
concentrated under reduced pressure. Silica gel column chromatog-
raphy (petroleum ether:ethyl acetate = 85:15) of the crude product
gave 13 as a colorless liquid (0.029 g, 88%): IR (CHCl3, cm−1) νmax
3445, 2926, 1695, 1456, 1158; 1H NMR (200 MHz, CDCl3) δ 1.11 (d,
J = 6.7 Hz, 6H), 1.46 (s, 18H), 1.54−1.69 (m, 2H), 2.70 (s, 6H),
3.87−4.26 (m, 2H) ppm; 13C NMR (125 MHz, CDCl3) δ 22.7, 28.5,
29.3, 31.9, 47.2, 79.1, 155.5 ppm; MS (ESI) m/z 353.21 (M + Na)+;
HRMS (ESI) m/z [M + H]+ Calcd for C17H35N2O4 331.2591, found
331.2591; [M + Na]+ Calcd for C17H34N2O4Na 353.2411, found
353.2409.
D i - t e r t - b u t y l ( ( 2 R , 4 R ) - p e n t a n e - 2 , 4 - d i y l ) b i s -
(methylcarbamate) (14). Colorless liquid (0.029 g, 88%): [α]D25
+2.10 (c 1.0, CHCl3); IR (CHCl3, cm−1) νmax 3445, 2926, 1695, 1456,
1158; 1H NMR (500 MHz, CDCl3) δ 1.09 (d, J = 6.8 Hz, 6H), 1.46 (s,
18H), 1.61−1.66 (m, 2H), 2.68 (s, 3H), 2.71 (s, 3H), 3.88−4.07 (m,
2H) ppm; 13C NMR (125 MHz, CDCl3) δ 22.7, 28.5, 29.7, 31.9, 49.5,
79.0, 79.4, 155.4, 155.6 ppm; MS (ESI) m/z 353.21 (M + Na)+;
HRMS (ESI) m/z [M + H]+ Calcd for C17H35N2O4 331.2591, found
331.2591; [M + Na]+ Calcd for C17H34N2O4Na 353.2411, found
353.2409.
ASSOCIATED CONTENT
■
S
* Supporting Information
Detailed spectral data (1H and 13C) for new compounds, X-ray
crystal structure, and the CIF files of 15 and 16, as well as
HPLC spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Fax +91-20-25902629. E-mail: pk.tripathi@ncl.res.in.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
V.J. thanks UGC New Delhi for research fellowships. We thank
Ms. S. Kunte for HPLC analysis. The authors thank CSIR, New
Delhi, for financial support as part of XII Five Year Plan under
title ORIGIN (CSC0108).
DEDICATION
■
Dedicated to Dr. Vijay Nair in recognition of his seminal
contributions to so many aspects of organic chemistry.
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(15) Diastereoselectivity was determined using chiral HPLC (see
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below.
I
dx.doi.org/10.1021/jo401722e | J. Org. Chem. XXXX, XXX, XXX−XXX