Abdul Rakeeb A. S. Deshmukh

Triphosgene: a versatile reagent for the synthesis of azetidin-2-ones

Abstract An efficient use of triphosgene, as an acid activator, for the synthesis of substituted azetidin-2-ones via ketene–imine cycloaddition reaction using various acids and imines have been described.

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.

A mild and efficient method for the preparation of acyl azides from carboxylic acids using triphosgene

Abstract An efficient use of triphosgene for the preparation of various acyl azides from carboxylic acids and sodium azide is described.

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.

Conformational preferences of α-functionalised keten-S,N-acetals: Potential role of SO and SS interactions in solution

PMR spectra of carbonyl compounds 2a-k reveal significant variations in the population of E and Z isomers on changing the solvent from CDCl3 to DMSO-d6. In non-polar media, the intramolecular N-H…. O hydrogen bonded form is exclusively observed. In DMSO-d6, the alternative Z form is also populated. A similar conformational switch is also noted in the corresponding thiones. Different interpretations are critically analysed. The most consistent explanation is suggested to involvean interplay of N-H….X hydrogen bonding and S…X attractive interaction (X = O,S) in these systems. Ab initio calculations support this interpretation.

Synthesis of N1-unsubstituted β-lactams: Introducing N1-(1′-thiophenyl)benzyl as an N-protecting group

Abstract A diastereoselective synthesis of (±) cis - β -lactams ( 5 & 6 ) via cycloaddition reaction of N 1 -(α-thiophenyl)benzyl imines ( 3 ) with acid chlorides ( 4 ) in the presence of triethyl amine is described. Deprotection of N 1 -(α-thiophenyl)-benzyl group was achieved in good yields by oxidation using potassium persulfate.

Conversion of carbonimidodithioates into unsymmetrical Di- and Tri- substituted ureas including urea dipeptides

Selective hydrolysis of carbonimidodithioates (3) leads to the thiocarbamates (4), which can be easily transformed to the unsymmetrical ureas (5) by treatment with the appropriate amines. This constitutes a synthesis of ureas without the use of phosgene or carbon monoxide.

Alkylation of Enaminothiones: What causes the observed stereoselectivity?

Abstract Alkylation of the enaminothiones 1 and 5 in the presence of base leads to the products 2 and 6 with preponderant or exclusive Z- configuration about the C C. Acid catalysed equilibration of 2 leads to a mixture in which the E- isomer predominates, whereas in the case of 6, the Z- form appears to be the thermodynamically favoured one.

4-formylazetidin-2-one as a useful building block for the formal synthesis of xylo -(2S,3R,4R ) -phytosphingosine and threo -(2S,3S) -sphingosine

Stereoselective formal synthesis of XYLO-(2 S,3 R,4 R)-phytosphingosine and THREO-(2 S,3 S)-sphingosine is described starting from an enantiopure formyl-substituted β-lactam. Grignard reaction of the N-Boc-protected-β-lactam carbonyl group, followed by further transformations, provides a common intermediate for XYLO-(2 S,3 R,4 R)-phytosphingosine and THREO-(2 S,3 S)-sphingosine.

Azetidin-2,3-dione synthon for stereoselective synthesis of cis- and trans-C-3-alkyl/aryl azetidin-2-ones

1,4-Bis-(4-methoxyphenyl)azetidin-2,3-dione has been prepared and used as a synthon for the stereoselective synthesis of C-3-alkyl/aryl azetidin-2-ones. Some of these are well known for their cholesterol absorption inhibitor activity. A regioselective Grignard reaction at a keto-group followed by highly stereoselective removal of the hydroxyl group via reductive removal of the xanthate ester is a key step in this synthesis. Base-induced isomerization of cis-azetidin-2-ones to the thermodynamically stable trans-isomer was also studied.