Veerappa B. Jigajinni

Hydrogenolysis of enol triflates; A new method for the reduction of ketones to methylene compounds

Abstract Hydrogenolysis of enol trifluoromethanesulphonates (enol triflates) gives the hydrocarbon in high yield; ketones can thus be converted to the corresponding methylene compounds in a two-step process under mild conditions.

The enantiospecific synthesis of (4S,5R)-and (4S,5S)-4,5-dihydroxydecanoic acid γ-lactones, proposed autoregulators from Streptomyces griseus

Abstract Both the (4S,5R)- and (4S,5S)-isomers of 4,5-dihydroxydecanoic acid γ-lactone, natural products and proposed autoregulators of Streptomyces Griseus, have been synthesised directly and in high yield from D-ribose via a common intermediate.

A novel and convenient synthesis of bis[arylthio]methanes

Abstract Bis[arylthio]methanes are produced in high yield on treatment of aryl chloromethyl sulphides with neutral alumina.

Enantiospecific synthesis of (+)-retronecine, (+)-crotonecine, and related alkaloids

Reaction of 2,3-O-isopropylidene-D-ribose (8) with diallylzinc gave a triol, which on treatment with periodate was converted into 5,6,7-trideoxy-2,3-O-isopropylidene-L-ribo-hept-6-enofuranose (10)(86%). Reaction with hydroxylamine hydrochloride in pyridine gave an oxime (11), which was treated with methanesulphonyl chloride in pyridine to yield 5,6,7-trideoxy-2,3-O-isopropylidene-4-O-methylsulphonyl-L-ribo-hept-6-enononitrile (12)(87% overall). Reduction with lithium aluminium hydride and cyclisation followed by treatment with benzyl chloroformate gave (2R,3S,4R)-2-allyl-1-benzyloxycarbonyl-3,4-isopropylidenedioxypyrrolidine (14), which on oxidation and subsequent reaction with diazomethane yielded (2R,3S,4R)-methyl (1-benzyloxycarbonyl-3,4-isopropylidenedioxypyrrolidin-2-yl)acetate (15b)(35%).A higher-yielding route to diester (15b) proceeded from 2,3-O-isopropylidene-D-erythrose (17), which was converted via its oxime into 2,3-O-isopropylidene-4-O-methylsulphonyl-D-erythrononitrile (19)(91%). Reaction with methyl bromoacetate and activated zinc, followed by base-catalysed cyclisation, gave (3S,4R)-methyl (3,4-isopropyl idenedioxypyrrolidin-2-ylidene)acetate (21)(78%), which with cyanoborohydride followed by N-acylation produced compound (15b)(87%).Treatment of diester (15b) with acid produced a γ;-lactone (23), which was deoxygenated via its Othiocarbonylimidazolide (24). Hydrogenolysis yielded (1R,5R)-2-oxa-6-azabicyclo[3.3.0] octan-3-one hydrochloride (6)(69% overall), which can be converted by known methods into (+)-retronecine (5) and other pyrrolizidine alkaloids.(1S,5R,8R)-Ethyl 8-hydroxy-3-oxo-2-oxa-6-azabicyclo[3.3.0]octane-6-carboxylate (28) was converted into its silyl ether (29), which underwent Dieckmann cyclisation to the pyrrolizidine (31), which is convertible by known methods into (+)-crotanecine (7).

Structure-property relationships in PMR-type polyimide resins: 4. Investigation of materials derived from diamino(diaryl)methanes☆

Abstract Polyimide oligomers (prepolymers) and resins of the PMR-15 type have been prepared from 5-norbornene-2,3-dicarboxylic half acid ester (NE), 3,3′,4,4′-benzophenonetetracarboxylic diester (BTDE) and a series of diamines including, and related to, 3,3′-diaminobenzophenone, viz. 3,3′-diaminobenzhydrol, 3-[(m,m′-diamino)benzhydryloxy]propyne (MDA-OMA) and 3,3′-diaminodiphenyl-α,α′-difluoromethane (FMDA). The PMR synthetic pathway (monomers→prepolymer→resin) has been assessed by dynamic mechanical thermal analysis. The Tg values for resins incorporating BTDE are significantly lowered compared to that for PMR-15 itself. The fluorine-containing PMR-15 type of resin (from FMDA) is of higher thermal stability than PMR-15 itself.

Structure-property relationships in PMR-type polyimide resins: 1. Novel anthraquinone-based PMR resins☆

Abstract Novel aromatic polyimides prepared via the polymerization of monomeric reactants (PMR) approach and incorporating anthraquinone diamines in the main chain have been characterized. Imidization and crosslinking reaction profiles have been delineated by d.m.t.a. and the high-temperature mechanical and thermal properties of the thermoset resins examined. Elevated glass transition temperatures (> 300°C) are apparent in some resins while impairment of mechanical integrity is not evident below 450°C. All resins show good thermal and thermo-oxidative stability.

Novel alumina-catalysed reactions of arylthioalkyl halides

ω-Chloroalkyl aryl sulphides rearrange to αω-bisaryl thioalkanes on treatment with alumina, and an alumina-catalysed equivalent of the Ullmann biphenyl synthesis is reported.

Michael additions to steroidal 1-ene-3-ones

Abstract A reactivity pattern was established for Michael addition of aryl thiolates to 17-acetoxy 5α-androst-1-en-3-one. An abnormal bicyclic bridged adduct was obtained in the reaction of thiourea.