Angular Alkylation of cis ‐Decalin Epoxides with C‐nucleophiles: Mechanism, scope, and limitations of a novel bridgehead functionalisation

The angular alkylation of cis ‐decalin epoxides like 5 or 7 can be achieved at C(8a) For convenience, the arbitrary numbering given for 5 ( Scheme I ) is used throughout the General Part ; for systematic names, see Exper. Part . in good yield by using CuI and a large excess of Grignard reagents without an sp 3 centre at C(2). The reaction proceeds via a carbenium‐ion intermediate which is stabilised by homoconjugative interaction with the adjacent double bond. Due to 1,3‐diaxial strain in the alkoxides resulting from alkylation or reduction at C(4a) of the epoxides 5 or 7 , the nucleophile is delivered selectively to C(8a). Grignard reagents possessing H‐atoms at C(β), transfer a hydride to the epoxide yielding the trans ‐decalol 11 ( Grignard reduction). The angular alkylation of 5 with allylic and benzylic Grignard reagents proceeds with good yield.