Electrophile-Induced C-C Bond Activation of Vinylcyclopropanes for the Synthesis of Z-Alkylidenetetrahydrofurans

Ganesh, Venkataraman and Kundu, Taraknath and Chandrasekaran, Srinivasan (2013) Electrophile-Induced C-C Bond Activation of Vinylcyclopropanes for the Synthesis of Z-Alkylidenetetrahydrofurans. In: JOURNAL OF ORGANIC CHEMISTRY, 78 (2). pp. 380-399.

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Abstract

We present a detailed study on the behavior of vinylcyclopropanes as masked donor acceptor system toward the stereoselective synthesis of Z-alkylidenetetrahydrofurans. Results of bromenium catalyzed indirect activation of C-C bond of vinylcyclopropanes and concomitant cyclization to alkylidenetetrahydrofuran and other heterocycles have been discussed. The stereoselective formation of the Z-isomer is strongly controlled by the extent of destabilization of one of the gauche conformers of the vinylcyclopropane. The ring-opening/cyclization step was found to be stereospecific as in the case of DA cyclopropanes. The activation of the C-C bond leads to a tight-carbocation intermediate, which is evident from the complete retention of the stereochemistry. The retention of configuration has been established by a necessary control experiment that rules out the possibility of a double inversion pathway. The present results serve as direct stereochemical evidence in support of a tight ion-pair intermediate versus the controversial S(N)2 pathway. A 2D potential energy scan has been carried out at B3LYP/6-31G(d) level theory to obtain the relative energies of the conformers. The Z-selectivity observed has been explained on the basis of the relative population of the conformers and modeling the intermediate and transition state involved in the reaction at M06-2x/6-31+G(d) level. Energy profile for the cyclization step was modeled considering various possible pathways through which cyclization can happen. The methodology has been successfully demonstrated on vinylcyclobutanes as well.

Item Type:	Journal Article
Publication:	JOURNAL OF ORGANIC CHEMISTRY
Publisher:	AMER CHEMICAL SOC
Additional Information:	Copyright for this article belongs to AMER CHEMICAL SOC, WASHINGTON,
Department/Centre:	Division of Chemical Sciences > Organic Chemistry
Date Deposited:	06 Mar 2013 11:06
Last Modified:	06 Mar 2013 11:06
URI:	http://eprints.iisc.ac.in/id/eprint/45950

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