A novel and efficient synthesis of bicyclo[2.2.2]octenones and sigmatropic shifts in ground and excited states: stereoselective route to cis-decalins and diquinane frameworks.

Vishwakarma Singh, Sridhar R Iyer, Shaikh M Mobin

Index: J. Org. Chem. 70(3) , 973-81, (2005)

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Abstract

A new and efficient synthesis of a variety of highly embellished bicyclooctenones having an endo-vinyl moiety and their sigmatropic shifts in ground and excited states leading to a stereoselective route to substituted cis-decalins and diquinane frameworks have been described. Functionalized bicyclo[2.2.2]octenones having an endo-vinyl group and a beta,gamma-enone chromophore were prepared by in situ generation of 6-chloromethyl-6-hydroxycyclohexadienones and cycloaddition with butadiene (also generated in situ) followed by manipulation of the adducts. The presence of contiguous carbonyl, hydroxyl, and chloromethyl groups in adducts led to the introduction of various alkyl groups alpha to the ketone in a stereoselective fashion. The 3,3-sigmatropic shift in the bridged bicyclic compounds gave the corresponding cis-decalins, whereas the triplet sensitized irradiation led to the formation of diquinanes as a result of a 1,2-acyl shift.