Download PDF
Synthesis 2009(11): 1829-1833  
DOI: 10.1055/s-0028-1088063
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Reactions of Morita-Baylis-Hillman Acetates with Huisgen Zwitterions: A Novel Strategy for the Synthesis of β-Amino Acid Derivatives

Anu Josea, Rony Rajan Paula, Resmi Mohana, Smitha C. Mathewa, A. T. Bijua, Eringathodi Sureshb, Vijay Nair*a
a Organic Chemistry Section, National Institute for Interdisciplinary Science and Technology (CSIR), Trivandrum 695019, India
Fax: +91(471)2491712; e-Mail: vijaynair_2001@yahoo.com;
b Analytical Science Discipline, Central Salt and Marine Chemicals Research Institute, Bhavanagar 364002, India

Further Information

Publication History

Received 16 January 2009
Publication Date:
27 April 2009 (online)

 PDF Download Permissions and Reprints All articles of this category

Abstract

The reaction of Huisgen Zwitterion with Morita-Baylis-Hillman acetates afforded β-amino acid derivatives.

Key words

Huisgen zwitterion - Morita-Baylis-Hillman acetate - β-amino acid

Although Huisgen zwitterion [¹] was known for nearly four decades, its synthetic potential remained largely unexploited except in some notable reactions like Mitsunobu Reaction. [²] In view of our longstanding interest in zwitter­ion chemistry, [³] recently we have explored the reactivity of Huisgen zwitterion towards various substrates like aldehydes, ketones, chalcones, diaryl 1,2-diones, quinones, isatins­, and allenes. [4-6] In this context it was of interest to examine the reactivity of Huisgen zwitterion towards Morita-Baylis-Hillman (MBH) adducts, [7] [8] which are unique substrates of great synthetic potential incorporating three manipulatable groups, namely, a hydroxy group, a double bond, and an electron-withdrawing group. In this paper, we describe the results of our investigations on the reaction of Huisgen zwitterion with MBH acetates.

The present studies were initiated by treating methyl 2-[(4-chlorophenyl)acetyloxymethyl]acrylate (1a) with diisopropyl azodicarboxylate and triphenylphosphine in THF at room temperature for 2 hours. The reaction afforded two products, namely, diisopropyl N-acetyl-N′-[3-(4-chlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3a) and diisopropyl N-[3-(4-chlorophenyl)-2-(methoxycarbonyl) allyl]hydrazine-1,2-dicarboxylate (4a) in 46% and 51% yield, respectively (Scheme  [¹] ).

Scheme 1 Reaction of Huisgen zwitterion with MBH acetate

The structure elucidation of 3a and 4a was accomplished by usual spectroscopic analysis. The ¹H NMR spectrum of the compound 3a showed singlet resonance signals at δ = 2.35 and 3.81 due to CH3CO group and CH3OCO groups. The NCH2 group was discernable at δ = 4.14-4.73 as a multiplet. In the ¹³C NMR spectrum the three ester carbonyl groups were present at δ = 169.4, 167.4 and 154.7 and that of the keto carbonyl group appeared at δ = 152.7, supporting the IR absorption observed in the region 1750-1700 and 1631 cm-¹. All other signals were also in good agreement with the proposed structure. The structure and stereochemistry of the compound was unambiguously established by single crystal X-ray analysis (Figure  [¹] ) of a representative compound, 3g.

Figure 1 Single crystal X-ray structure of di-tert-butyl N-acetyl-N′-[3-(3,4-dichlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3g)

The IR spectrum of the compound 4a showed strong absorptions at 3308 and 1703-1722 cm-¹ due to NH group and the ester carbonyl groups, respectively. The ¹H NMR showed singlets at δ = 4.5 and 6.71 due to NCH2 and NH groups. In the ¹³C NMR spectrum signals due to the ester carbonyl groups were discernable at δ = 155.5, 156.3, and 167.7. Other signals were also in good agreement with the proposed structure.

The mechanism of the reaction may be rationalized by invoking an SN2′ process, involving the Huisgen zwitterion and the Morita-Baylis-Hillman acetate (Scheme  [²] ). Evidently, the first step of the reaction is the formation of Huisgen zwitterion by the addition of triphenylphosphine to diisopropyl azodicarboxylate. The SN2′ displacement of the acetate from 1a induced by Huisgen zwitterion would lead to the formation of the cationic intermediate 5. The attack of the acetate on 5 followed by rearrangement and the elimination of Ph3PO, would result in the formation of diisopropyl N-acetyl-N′-[3-(4-chlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3a). Similarly by the addition of hydroxy anion to 5, an intermediate 7 is formed, and the latter on elimination of tri­phenylphosphine oxide would deliver diisopropyl N-[3-(4-chlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4a).

Scheme 2 Mechanistic rationale for the formation of hydrazine-1,2-dicarboxylates 3a and 4a

As disclosed inTable 1, the reaction was found to be general with various Morita-Baylis-Hillman acetates and Huisgen zwitterions.

Table 1 Hydrazine-1,2-dicarboxylates 3 and 4 Prepared

3, 4 R¹ R² X Yield (%)
3 4
a 4-ClC6H4 i-Pr CO2Me 46 51
b 4-CF3C6H4 Et CO2Me 57 41
c 3-ClC6H4 Et CO2Me 38 49
d Ph i-Pr CO2Me 35 56
e Ph i-Pr CN 57 37
f 4-FC6H4 t-Bu CO2Me 37 46
g 3,4-Cl2C6H3 t-Bu CO2Me 58 30
h Ph Et CO2Me 35 49
i 4-MeC6H4 i-Pr CO2Me 40 36
j 4-BrC6H4 i-Pr CO2Me 54 40

In conclusion, herein we have reported a facile C-N bond-forming reaction, which incidentally constitutes the first example of the participation of Huisgen zwitterions in an SN2′ reaction.

Melting points were recorded on a Büchi melting point apparatus and are uncorrected. NMR spectra were recorded at 300 MHz (¹H) and 75 MHz (¹³C) respectively on a Bruker Avance DPX-300 MHz NMR spectrometer. Chemical shifts are reported (δ) relative to TMS (¹H) and CDCl3 (¹³C) as the internal standards. Coupling constants (J) are reported in Hertz (Hz). High-resolution mass spectra were recorded under EI/HRMS (at 5000 resolution) or FAB+/HRMS using Jeol JMS 600H mass spectrometer. IR spectra were recorded on Nicolet Impact 400D FT-IR spectrophotometer. Commercial grade solvents were distilled prior to use.

Reactions of Morita-Baylis-Hillman Acetates with Huisgen Zwitterions; General Procedure

The Morita-Baylis-Hillman acetate 1 (1 equiv) dissolved in THF (5 mL) was treated with the respective azodicarboxylate 2 (1.2 equiv) and Ph3P (1.2 equiv) at r.t. for 2 h under N2. The solvent was removed under reduced pressure and the crude reaction mixture was purified by column chromatography using silica gel (60-120 mesh) and hexane-EtOAc.

Diisopropyl N -Acetyl- N ′-[3-(4-chlorophenyl)-2(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3a)

Yield: 46%.

IR (KBr): 2983, 1750-1700, 1631, 1582 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.18-1.34 (m, 12 H), 2.35 (s, 3 H), 3.81 (s, 3 H), 4.24-4.73 (m, 2 H), 4.88-5.00 (m, 2 H), 7.26-7.38 (m, 4 H), 7.83 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.3, 21.6, 21.7, 22.1, 25.1, 42.8, 51.5, 70.2, 71.7, 126.7, 127.1, 128.8, 130.9, 132.8, 135.5, 140.4, 143.5, 152.7, 154.2, 167.4, 169.4.

HRMS (EI): m/z calcd for C21H27ClN2O7: 454.1507; found: 454.0291.

Diisopropyl N ′-[3-(4-Chlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4a)

Yield: 51%.

IR (KBr): 3309, 2983, 1722-1703 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.14-1.25 (m, 12 H), 3.74 (s, 3 H), 4.5 (s, 2 H), 4.77- 4.92 (m, 2 H), 6.71 (s, 1 H), 7.13-7.28 (m, 4 H), 7.72 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.6, 21.9 45.5, 51.7, 69.4, 70.1, 128.3, 128.7, 129.7, 130.7, 133.5, 135.1, 142.3, 155.5, 156.3, 167.7.

HRMS (EI): m/z calcd for C19H25ClN2O6: 412.1401; found: 412.1396.

Diethyl N -Acetyl- N ′-[3-(4-trifluoromethylphenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3b)

Yield: 57%.

IR (KBr): 1715 (br), 1242, 1103 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.17-1.25 (m, 6 H), 2.35 (s, 3 H), 3.82 (s, 3 H), 4.10-4.16 (m, 4 H), 4.53-4.74 (m, 2 H), 7.38 (m, 2 H), 7.67 (d, J = 8.0 Hz, 2 H), 7.89 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 13.9, 14.1, 14.4, 25.1, 43.1, 52.3, 62.7, 63.6, 124.9, 125.4, 128.7, 128.9, 129.7, 131.2, 137.9, 142.9, 153.1, 154.5, 167.3, 169.3.

HRMS (EI): m/z calcd for C20H23F3N2O7: 460.1456; found: 454.1457.

Diethyl N ′-[3-(4-Trifluoromethylphenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4b)

Yield: 41%.

IR (KBr): 3421, 2999, 1755-1697 (br), 1263 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.22-1.30 (m, 6 H), 3.84 (s, 3 H), 4.11-4.23 (m, 4 H), 4.57 (s, 2 H), 6.78 (s, 1 H), 7.54 (m, 2 H), 7.65 (d, J = 8.1 Hz, 2 H), 7.87 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 13.9, 14.1, 14.4, 25.1, 43.1, 52.3, 62.7, 63.6, 124.9, 125.4, 128.7, 128.9, 129.7, 131.2, 137.9, 142.9, 153.1, 154.5, 167.3, 169.5.

HRMS (EI): m/z calcd for C18H12F3N2O6: 418.1461; found: 418.1463.

Diethyl N -Acetyl- N ′-[3-(3-chlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3c)

Yield: 38%.

IR (KBr): 1713, 1240 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.17-1.27 (m, 6 H), 2.36 (s, 3 H), 3.80 (s, 3 H), 4.11-4.24 (m, 4 H), 4.34-4.74 (m, 2 H), 7.06-7.46 (m, 4 H), 7.55 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 14.0, 14.5, 14.6, 25.2, 43.9, 125.9, 126.5, 130.4, 131.5, 131.9, 143.8, 144.0, 153.2, 154.7, 162.2, 167.8, 169.5.

HRMS (EI): m/z calcd for C19H23ClN2O7: 426.1217; found: 426.1219.

Diethyl N ′-[3-(3-Chlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4c)

Yield: 49%.

IR (KBr): 3424, 2983, 1759-1699 (br), 1487 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.16-1.29 (m, 6 H), 3.74 (s, 3 H), 4.03-4.15 (m, 4 H), 4.52 (s, 2 H), 6.72 (s, 1 H), 7.00-7.33 (m, 4 H), 7.75 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 14.2, 14.5, 46.7, 52.2, 61.9, 62.5, 115.6, 126.9, 130.5, 131.5, 142.8, 155.9, 162.0, 164.0.

HRMS (EI): m/z calcd for C17H21ClN2O6: 384.1107; found: 384.1111.

Diisopropyl N -Acetyl- N ′-[3-phenyl-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3d)

Yield: 35%.

IR (KBr): 1712, 1249 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.16-1.28 (m, 12 H), 2.30 (s, 3 H), 3.81 (s, 3 H), 4.53-4.80 (m, 4 H), 4.87-4.99 (m, 2 H), 7.38 (m, 5 H), 7.90 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.1, 21.5, 21.9, 25.0, 52.0, 70.0, 70.4, 71.5, 128.5, 129.1, 129.4, 129.5, 145.0, 152.7, 154.1, 167.7, 169.3.

HRMS (EI): m/z calcd for C21H28N2O7: 420.1910; found: 420.1907.

Diisopropyl N ′-[3-Phenyl-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4d)

Yield: 56%.

IR (KBr): 3211, 2991, 1753-1698 (br) cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.20-1.32 (m, 12 H), 4.11 (s, 3 H), 4.62 (s, 2 H), 4.92-4.98 (m, 2 H), 6.62 (s, 1 H), 7.37 (s, 5 H), 7.86 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.7, 21.8, 21.9, 43.3, 52.0, 70.0, 70.2, 70.3, 128.9, 129.3, 134.4, 155.6, 156.4, 166.5.

LRMS-FAB: m/z calcd for C19H26ClN2O6 (M + H)+: 379.18; found: 379.20.

Diisopropyl N -Acetyl- N ′-[(3-phenyl-2-cyano)allyl]hydrazine-1,2-dicarboxylate (3e)

Yield: 57%.

IR (KBr): 3037, 2218, 1762-1703 (br), 1361 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.19-1.33 (m, 12 H), 2.56 (s, 3 H), 4.95-5.04 (m, 2 H), 7.40-7.42 (m, 5 H), 7.77 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.3, 21.6, 25.1, 45.7, 53.1, 70.5, 72.1, 106.2, 109.9, 117.9, 119.4, 128.7, 129.8, 130.6, 132.6, 146.1, 147.8, 152.4, 153.3, 154.0, 169.7.

LRMS (+FAB): m/z calcd for C20H23ClN3O5 (M + H)+: 388.18; found: 388.21.

Diisopropyl N -[(3-Phenyl-2-cyano)allyl]hydrazine-1,2-dicarboxylate (4e)

Yield: 37%.

IR (KBr): 3413, 2988, 2216, 1752-1715 (br), 1481, 1381 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.25-1.33 (m, 12 H), 4.43-4.53 (m, 2 H), 4.89-5.05 (m, 2 H), 6.89 (s, 1 H), 7.41-7.75 (m, 5 H), 7.76 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.6, 21.9, 52.5, 69.7, 69.9, 106.5, 128.8, 128.9, 130.5, 132.9, 154.8, 156.4.

LRMS-FAB: m/z calcd for C18H23N3O4 (M + H)+: 346.17; found: 346.20.

Di- tert -butyl N -Acetyl- N ′-[3-(4-fluorophenyl)-2-(methoxycarbonyl)allyl]hydrazene-1,2-dicarboxylate (3f)

Yield: 32%.

IR (KBr): 1741 (br), 1379, 1240, 1103 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.41-1.50 (m, 18 H), 2.30 (s, 3 H), 3.81 (s, 3 H), 4.48-4.70 (m, 2 H), 7.06-7.4 7 (m, 4 H), 7.84 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 25.3, 25.4, 27.7, 28.0, 28.2, 29.4, 30.8, 42.1, 43.6, 51.5, 52.1, 115.8, 126.7, 130.7, 131.9, 143.6, 153.2, 164.2, 167.9, 169.9.

LRMS-FAB: m/z calcd for C23H31FN2O7 (M + H)+: 467.21; found: 467.22.

Di- tert -butyl N ′-[3-(4-Fluorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4f)

Yield: 46%

IR (KBr): 2985, 1750, 1379, 1242, 1105 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.42-1.46 (m, 18 H), 3.81 (s, 3 H), 4.57 (s, 2 H), 6.36 (s, 1 H), 7.02-7.42 (m, 4 H), 7.79 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 14.1, 22.6, 28.1, 29.1, 30.7, 31.7, 52.0, 81.2, 115.4, 115.7, 127.3, 131.5, 139.0, 142.3, 155.0, 161.3, 167.9.

LRMS-FAB: m/z calcd for C21H29FN2O6 (M + H)+: 425.20; found: 425.21.

Di- tert -butyl N -Acetyl- N ′-[3-(3,4-dichlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3g)

Yield: 58%.

IR (KBr): 3037, 2985, 1762, 1745, 1703, 1382, 1286, 1240 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.43-1.51 (m, 18 H), 2.36 (s, 3 H), 3.82 (s, 3 H), 4.45-4.63 (m, 2 H), 7.29 (d, J = 9 Hz, 1 H), 7.45 (d, J = 9 Hz, 1 H), 7.60 (s, 1 H), 7.75 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 22.7, 25.3, 26.9, 27.7, 27.8, 42.2, 52.3, 81.5, 83.8, 128.0, 129.0, 130.5, 131.6, 138.7, 142.2, 151.7, 153.2, 167.2, 169.9.

LRMS-FAB calcd for C23H30Cl2N2O7 (M + H)+: 517.14; found: 517.15.

Di- tert -butyl N ′-[3-(3,4-Dichlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4g)

Yield: 30%.

IR (KBr): 3415, 2975, 1751, 1741, 1712, 1481, 1381, 1250, 1105 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.45 (s, 18 H), 3.82 (s, 3 H), 4.54 (s, 2 H), 6.4 (s, 1 H), 7.44 (d, J = 9 Hz, 2 H), 7.52 (s, 1 H), 7.71 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 14.2, 19.4, 20.9, 22.6, 28.1, 52.2, 81.0, 129.3, 130.5, 131.2, 132.8, 134.5, 140.7, 154.8, 161.3, 170.8.

LRMS-FAB: m/z calcd for C21H28Cl2N2O6 (M + H)+: 475.13; found: 475.02.

Diisopropyl N -Acetyl- N ′-[3-(4-methylphenyl)-2(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3i)

Yield: 40%.

IR (KBr): 3314, 2982, 1739-1723, 1634, 1109 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.12-1.44 (m, 12 H), 2.30 (s, 3 H), 2.37 (s, 3 H), 3.80 (s, 3 H), 4.52-4.80 (m, 2 H), 4.75-4.99 (m, 2 H), 7.15-7.32 (m, 4 H), 7.87 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.2, 21.4, 21.6, 21.9, 46.3, 51.9, 69.3, 69.7, 69.9, 126.1, 128.3, 128.8, 129.2, 129.5, 131.5, 139.2, 143.8, 155.6, 156.3, 168.1.

LRMS-FAB: m/z calcd for C22H30N2O7 (M + H)+: 435.21; found: 435.37.

Diisopropyl N ′-[3-(4-Methylphenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4i)

Yield: 36%.

IR (KBr): 3309, 2983, 1730-1703 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.20-1.35 (m, 12 H), 2.36 (m, 3 H), 3.80 (s, 3 H), 4.64 (s, 2 H), 4.82-5.00 (m, 2 H), 6.71 (s, 1 H), 7.12-7.31 (m, 4 H), 7.84 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.2, 21.4, 21.9, 29.6, 46.3, 51.9, 69.4, 69.7, 70.0, 72.4, 126.1, 128.4, 128.9, 129.5, 131.5, 139.2, 143.8, 155.6, 168.1.

LRMS-FAB: m/z calcd for C20H28N2O6 (M + H)+: 391.18; found: 391.97

Diisopropyl N -Acetyl- N ′-[3-(4-bromophenyl)-2(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3k)

Yield: 54%.

IR (KBr): 3334, 2983, 1788-1711, 1634, 1587 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.14-1.33 (m, 12 H), 2.36 (s, 3 H), 3.81 (s, 3 H), 4.52-4.62 (m, 2 H), 4.90-4.96 (m, 2 H), 7.15-7.55 (m, 4 H), 7.81 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.3, 21.6, 21.8, 22.0, 25.3, 29.7, 42.8, 51.7, 70.8, 71.7, 123.8, 126.8, 130.2, 133.4, 140.5, 143.7, 152.7, 154.2, 167.7, 169.5.

HRMS (EI): m/z calcd for C21H27ClN2O7: 499.1002; found: 499.1010.

Diisopropyl N ′-[3-(4-Bromophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (4k)

Yield: 40%.

IR (KBr): 3310, 2983, 1730-1703 cm-¹.

¹H NMR (300 MHz, CDCl3): δ = 1.21-1.36 (m, 12 H), 3.81 (s, 3 H), 4.57 (s, 2 H), 4.86-4.99 (m, 2 H), 6.72 (s, 1 H), 7.29-7.52 (m, 4 H), 7.77 (s, 1 H).

¹³C NMR (75.47 MHz, CDCl3): δ = 21.7, 21.9, 46.1, 51.7, 69.5, 70.6, 128.4, 128.8, 129.8, 131.0, 133.7, 135.3, 142.4, 155.8, 156.4, 167.8.

HRMS (EI): m/z calcd for C19H25BrN2O6: 457.0896; found: 457.0912.

Acknowledgment

V.N. acknowledges the DST support in the form of a Raja Ramanna Fellowship. Financial assistance to S.C.M. and B.A.T. from the Council of Scientific and Industrial Research (CSIR), Government of India, is acknowledged. The authors also thank Mrs. Saumini Mathew for recording NMR spectra and Mrs. S. Viji for mass spectral analysis.

   Permissions and Reprints All articles of this category

Scheme 1 Reaction of Huisgen zwitterion with MBH acetate

Figure 1 Single crystal X-ray structure of di-tert-butyl N-acetyl-N′-[3-(3,4-dichlorophenyl)-2-(methoxycarbonyl)allyl]hydrazine-1,2-dicarboxylate (3g)

Scheme 2 Mechanistic rationale for the formation of hydrazine-1,2-dicarboxylates 3a and 4a