'-trimethylcyclohex-2'-enyl and l'-enyl) pentanoatee &and g were submitted to both: Lewis acid (tin (IV) tetrachloride) and free radical (manganese (III) acetate) cyclization conditions. The structures of the different products are discussed in terms of the reaction mechanisms.
Lewis acid and photochemically mediated cyclizations have been commonly used for the construction of a great number of substituted decalin intermediates' for the synthesis of important natural products. More recently, free radical cyclizations of halo alkanea have also developed into a powerful method for the synthesis of polycyclic compounds. However, their reductive last step render somewhat less versatile products. The alternative Mn(II1) oxidative cyclizations of S-keto esters seems to offer an interesting alternative to overcome these limitations. 2
We were particularly interested in the outcome of such Mn(II1) mediated cyclixation reactions of unsaturated S-keto esters like 1, from the point of view of both, the regiochemistry and stereochemistry of the reaction, in comparison with the behavior of the same compound under Lewis acid catalysis.
Scheme 1
Compounds &and 2 were easily prepared from alpha and beta ionone respectively,