Baburao M. Bhawal

Asymmetric synthesis of azetidin-2-ones by [2+2] cycloaddition using chiral imines derived from d-(+)-glucose

Abstract Asymmetric synthesis of β-lactams by the [2+2] cycloaddition of ketenes with chiral imines derived from d -(+)-glucose was carried out; predominantly cis-β-lactams were formed with very high diastereoselectivity. The stereochemistry at C-3 and C-4 was established as 3S and 4R from the known absolute configuration of the sugar moiety.

Application of (+)-(1S,2S)-2-amino-1-phenylpropan-1,3-diol in the formal total synthesis of carbapenems, novel 4-cyano-β-lactams and β-hydroxy aspartates

Abstract The imines derived from (+)-(1S,2S)-2-amino-1-phenylpropan-1,3-diol furnished cis-β-lactams stereoselectively on the Staudinger reaction. These homochiral cis-β-lactams were converted in to cis-β-lactams possessing aminol side chain at C-4. These aminols were efficiently transformed in to novel 4-cyano-cis-β-lactams, 4-acetoxy-β-lactam (which are well proven starting materials in the synthesis of carbapenem antibiotics) and advanced starting materials for the synthesis of β-hydroxy aspartates.

Stereoselective synthesis of homochiral pyrrolidinones and cis, cis-bis-β-lactams from (+)-(1S,2S)-2-amino-1-phenylpropan-1,3-diol

Abstract The homochiral β-lactams described in the preceding paper undergone an acid catalyzed rearrangement to 4-aminopyrrolidinones 2a-e in excellent yields. A diastereoselective synthesis of cis,cis-bis-β-lactams 13 & 14 has been achieved by using imines bearing a β-lactam back bone in good yields and good to excellent selectivities.

An efficient synthesis of cis-3-hydroxy-4-phenyl-β-lactams: Precursor for taxol side chain

Abstract Chiral ketene precursors derived from naturally occurring (+)-3-carene have been used for the synthesis of β-lactams via the Staudinger reaction. The major diastereomer 5a was separated by crystallization and converted in very good yield into (3 R , 4 S )-3-hydroxy-4-phenyl- β -lactam, an advanced intermediate towards the taxol side chain.

Stereoselective Synthesis of cis-Bis-β-lactams Linked with an Ethylene Bridge

Abstract An efficient synthesis of (±)-cis-bis-β-lactams (5 and 6) via cycloaddition reaction of bisimines (3a–c) with acid chlorides (4) in the presence of triethylamine in very good yield is described.

Unique zeolite-catalyzed synthesis of nitroketene S,N-acetals

Abstract Dimethyl carbonimidodithioates (4a–g, 7a–c) derived from various primary amines and amino acid esters [glycine, (L)-alanine and (L)-phenylalanine] have been condensed with nitromethane in the presence of the rare-earth exchanged zeolite RE(70%)Na Y to give the S,N-acetals (5a–g, 8a–c). Mercuric chloride catalyzed hydrolysis of these (8a–c) has led to the nitroacetyl derivatives (9a–c). The glycine derivative (7a) gives a dimeric product (11) when heated alone with the zeolite.

Ephedrine derived reusable chiral auxiliary for the synthesis of optically pure 3-hydroxy-4-aryl-β-lactams

Abstract The diastereoselective synthesis of various β-lactams has been achieved using a chiral acid auxiliary derived from (−)-ephedrine. An efficient acid-catalyzed cleavage of the chiral auxiliary from these β-lactams to afford 3-hydroxy-4-aryl-cis-β-lactams, which are precursors for analogues of the taxol side chain, is described.

An efficient use of Oppolzer sultam for Diastereospecific Synthesis of cis-β-Lactams

Abstract Diastereospecific Synthesis of cis-β-Lactams (6a-g) has been achieved in ketene-imine cycloaddition reaction (Staudinger reaction) by using homochiral ketene precursors 3 and 4 derived from Oppolzer sultam, in very good yields.

Modulating steric effects in diastereoselective Staudinger reaction: Synthesis of optically pure cis-β-lactams

Abstract Diastereoselection in the synthesis of β-lactams ( 14 and 15 ) via ketene-imine cycloaddition (Staudinger reaction) using different chiral auxiliaries has been examined. While sterically demanding imines derived from bicyclic aldehyde ( 1 ) with a β chiral centre provided excellent selectivity, use of imines derived from bicyclic aldehyde ( 17 ) with a γ chiral centre was not effective. Improvement of stereoselectivity was also sought using imines ( 6 and 7 ) derived from chiral amines ( 2d,e ) and chiral aldehyde ( 1 ). The bicyclic terpenoid skeleton of the chiral auxiliary in 1 was dismantled by ruthenium tetroxide oxidation to give multiply functionalized β-lactams 23a-d in good yield.

First total synthesis of (±)-brasiliquinone B

Abstract Brasiliquinone B (2) was synthesized from 7-methoxy-1-tetralone in 8 steps making use of Friedel-Crafts alkylation as a key step.