Ranganathan Viswajanani

Reduction of quinolines to 1,2,3,4-tetrahydro derivatives employing a combination of NaCNBH3 and BF3.OEt2

A regiospecific reduction of quinolines (and 1,10-phenanthroline) into the corresponding 1,2,3,4-tetrahydro derivatives using a combination of sodium cyanoborohydride and boron trifluoride etherate in refluxing methanol is described. Under the same conditions indole and acridine reduced to the corresponding dihydroderivatives, whereas acyl group transfer from oxygen to nitrogen atom is also noticed in the case of 8-acyloxyquinolines.

Chemoselective reductive deoxygenation of α,β-unsaturated ketones and allyl alcohols

A simple and convenient procedure for a highly chemoselective reductive deoxygenation of α,β-unsaturated ketones and allyl alcohols to olefins by sodium cyanoborohydride and boron trifluoride etherate in dry THF is described.

A simple strategy for spirocyclopentannulation of cyclic ketones. Formal total synthesis of (±)-acorone

A general and simple methodology for spirocyclopentannulation of cyclic ketones (or 4,4-disubstituted cyclopentenones from acyclic ketones) and its application in the synthesis of the spirodienone 7 via a prochiral precursor constituting a formal total synthesis of (+/-)-acorone (6), are described.

A new tetrahydrofurannulation via tandem radical cyclisation reaction-reductive deoxygenation sequence

Treatment of bromoketals 2, derived from allyl alcohols 1, with tributyltin chloride, sodium cyanoborohydride and AIBN furnishes the tetrahydrofurannulated products 3 via a 5-exo-trig radical cyclisation reaction followed by reductive cleavage of ketal 4.

A mild and simple procedure for the reductive cleavage of acetals and ketals

A convenient, mild and simple procedure, employing sodium cyanoborohydride in the presence of either catalytic or stoichiometric amount of boron trifluoride etherate in dry THF, for the reductive cleavage of the acetals and ketals is described.

TRIBUTYLTIN CHLORIDE-SODIUM CYANOBOROHYDRIDE MEDIATED TANDEM RADICAL CYCLISATION-REDUCTIVE DEMETHOXYLATION SEQUENCE

Reaction of the bromoketals 3, 7a-g and 11 with tri-n-butyltin chloride and sodium cyanoborohydride in the presence of a catalytic amount of AIBN furnished the ethers 5, 8a-g and 13 via a tandem sequence comprising of a radical cyclisation reaction and tri-n-butylhalostannane and sodium cyanoborohydride mediated reductive demethoxylation of the resulting cyclic ketals.

Stereospecific construction of stereogenic vicinal quaternary carbon atoms. Enantiospecific synthesis of (+)-valerane

Stereo- and enantiospecific synthesis of (+)-valerane starting from R-carvone utilising orthoester Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions for the construction of the two vicinal quaternary carbon atoms is described. Copyright (C) 1996 Elsevier Science Ltd.

A radical cyclisation based cyclopentenone annulation of allyl alcohols

A four-step cyclopentenone annulation reaction of allylic alcohols employing a 5-exo-trig radical cyclisation reaction of mixed allyl methyl ketals of bromoacetone as the key step is described. The annulated product 12b obtained from 2,3-dimethylcyclohexenol has been further elaborated into (±)-epibakkenolides employing a 5-exo-dig radical cylisation reaction based α-spiro-β-methylene-γ-butyrolactone annulation methodology.

Stereoselective construction of vicinal stereogenic quaternary carbon atoms. Enantiospecific approaches to (+)-valerane

Two enantiospecific routes to (+)-valerane starting from (R)-carvone, using a combination of Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions for the stereoselective generation of the vicinal stereogenic quaternary carbon atoms, are described. Thus, orthoester Claisen rearrangement of 3-methylcarveol 6 furnishes the ester 9 containing the first quaternary carbon atom. Intramolecular cyclopropanation of the diazo ketone 10 derived from the ester 9, followed by regioselective reductive cyclopropane cleavage, generates the hydrindanone 11 containing all stereocentres of valerane. Ring expansion of the hydrindanone to tetralone and further reductions transform 11 into (+)-valerane 2. In another direction, homologation of the acid 5 followed by intramolecular cyclopropanation of the diazo ketone 24 and regioselective cyclopropane ring cleavage lead to valerenone 25, which is transformed into (+)-valerane.

Cyclopentaannulation of allyl alcohols via a radical cyclisation reaction. Total synthesis of 4-epibakkenolide-A

A four step cyclopentaannulation methodology starting from allyl alcohols using 5-exo-trig radical cyclisation as the key reaction, and its application to the total synthesis of 4-epibakkenolide is described.