Amareshwar Chatterjee

Conformational and steric requirements of the side chain for sulphur participation in benzthiepin derivatives

Abstract Attempted ring expansion of some benzthiepin derivatives resulted in the formation of benzthiophens such as (3a,b) and (3d,e). A probable mechanism for this transformation has been presented.

Synthesis of 4-methyl-5-methoxyindan-1-one

Abstract PPA and Friedel-Crafts cyclizations of the bromo-acid (mixture) obtained by nuclear bromination of VII furnished three isomeric bromoketones characterised as XII, XI and XVI. The ketones XII and XI on catalytic debromination afforded 6-methoxy-7-methylindan-1-one (III) which on catalytic hydrogenolysis and subsequent oxidation furnished 4-methyl-5-methoxyindan-1-one (V). An unambiguous synthesis of this title compound (V) was also achieved using 2-methyl-3-methoxybenzyl chloride (XXIII) as the starting material. The change in the intensities of the K-bands of some indanone derivatives have been discussed in the light of buttressing effect.

Carbanion addition to acetylenes : An efficient stereoselective route to α-methylene-γ-lactams

Abstract Intramolecular addition of carbanions, derived from the acetylenic amides (5b,d) , (7) and (9) has been shown to be highly stereoselective leading to the α-methylene-γ-lactam derivatives (6a,b) , (8a,b) and (10) .

Total synthesis of ring-c aromatic 18-nor steroid

Abstract The total synthesis of (±)-11-methoxy-18-nor-5χ and 5β-androsta-8(9),11,13(14)-triene-3,17-dione is reported.

Studies on nucleophilic ring opening of some epoxides in polar protic solvents—I

Abstract The epoxides of the type 4 undergo ring-opening with carbanions; without exception, the nucleophiles attack at C-1 in spite of the increased steric hindrance at the site (as in epoxides 4b and 4e having peri-substituents). Interaction of the epoxide 4b with the anion of diethyl methylmalonate in refluxing t-butanol afforded, besides other products, the novel cyclopropane carboxylic acid 12 . What is more significant is that although the formation of the trans-lactone on the whole is favoured in the ring opening of epoxides 4 , at least in two cases, 4b and 4c , there is considerable formation of cis-lactones, a result that remains unexplained. Attempted synthesis of the model cis-lactone 3c always resulted in the formation of a 1:1 mixture of the cis- 3c and the trans-lactone 2a . The stereochemistries of the cis- and the trans-lactones described in this paper have been unambiguously established from the position of the 3a-proton signals of these γ-lactones in their NMR spectra.

Efficient syntheses of some 1-naphthylalkyl ketones and studies on their autooxidation in basic medium

Abstract Birch reductions of 4,6-dimethoxy-1-naphthylalkyl ketones 1 provided in fair to good yields the demethoxylated products, 6-methoxy-1-naphthylalkyl ketones 2(a–g), not easily accessible by other procedures. Autooxidation of these ketones in basic medium afforded the diketones 6(a–c), the acid 2h, and interestingly the phenol 5. Extension of this reduction to the related tricyclic ketone 8 afforded 9a, the phenolic ketone 9b; and significantly the dihydrocoumarin derivative 10 as a result of autooxidation of 9a. The mechanisms for demethoxylation and autooxidation have been discussed.

Role of remote heteroatoms and nature of the reducing agents on the stereochemical course of reductions of the carbon–nitrogen π-bond of a new class of tetrahydropyridines

Total syntheses of the tetrahydropyridine derivatives (3a–f) and the steroid analogue (1b) are reported. Catalytic reductions of the above imines have been found to be highly stereoselective, yielding only the trans-amine in most cases. Lithium aluminium hydride reductions of the above imines (3a–e), (1b), and (3f–g), however, showed cis-stereoselectivity; the imines (3a–b) and (1b) afforded only the cis-amines under these conditions. Sodium borohydride reductions of the imines (3a–g) gave conflicting results, the imines (3a–b) and (3f–g) furnishing stereoselectively the trans-amines. Metal–ammonia reductions of the imines (3a–b) and (3f), having a carbocyclic B ring, gave a stereoisomeric mixture of amines; similar reduction of the imines (3c–d) with an oxygen atom in ring B, provided, interestingly, the corresponding trans-amines as the predominant product (84–94%). Reasons for the different stereochemical results observed in the reductions of the imines (3a–g) with various reducing agents have been briefly discussed. The stereochemical assignments of the amines (14)–(15) and (16)–(17) were secured from their 1H and 13C n.m.r. spectra, and also from 1H n.m.r. spectra of their N-acetyl derivatives.

Carbon-carbon cyanoethylation of anisole and its derivatives: Synthesis of a potential intermediate for ring-C aromatic steroid

Cyanoethylations of o-cresyl methyl ether, anisole, α-naphthyl methyl ether, resorcinol dimethyl ether, and 1,7-dimethoxynaphthalene provided the desired products in reasonably good yields: synthetic applications are indicated.

An interesting ring contraction of a class of bromohydrins and trans-dibromides

Abstract An efficient ring contraction of stereoisomeric 1,2-benzo-4-bromo-3-hydroxycyclohept-1-ene and their derivatives (1a-e) to (2a-c) is reported, and a probable mechanism for this ring contraction has been suggested.

Nucleophilic ring opening of epoxides by carbanions. Novel formation of cyclopropane derivatives in a non-polar solvent

Abstract Nucleophilic ring-opening of epoxides 2(a-d) with carbanions of different steric requirements under refluxing benzene afforded a single stereoisomer of the cyclopropane derivatives 4. The same reaction under refluxing ethanol gave the normal products, i.e. the trans-lactones 6. Mechanism and high stereoselectivity observed in the novel cyelopropane formation, and regiospecific cleavage of the cyclopropane carboxylic acids (in4) have also been discussed in detail.