1,3-Elimination with rearrangement during ester pyrolysis. A simple route to protoadamantene and 2,4-didehydroadamantane

Abstract

Pyrolysis of 2-adamantyl methane- or toluene-p-sulphonate (16) affords a mixture (2 :3) of protoadamantene (17) and 2,4-didehydroadamantane (18) in 95% yield. Hydroboration of (17) gives a mixture of 4-[(20), (21)] and 5-[(24), (25)] protoadamantanols. Epoxidation of protoadamantene gives a mixture (6 : 1) of the exo-(26) and endo-(27), epoxides the former rearranging spontaneously to 2a,4a-dihydroxyadamantane (28). Protoadamantan-5-one (23) with lithium aluminium hydride gives a 95 : 5 endo : exo alcohol mixture, but lithium–ammonia gives 70 : 23 exo : endo alcohols.