HIGHLY STEREOSPECIFIC ISOMERIZATION OF OXIRANES INTO ALLYLIC ALCOHOLS BY MEANS OF ORGANOALUMINUM AMIDES

Organoaluminum reagents of type R1R2NAlR2 allow highly stereospecific oxirane ring opening producing allylic alcohols under mild conditions. trans-Epoxycyclododecane is converted to (-E)-2-cyclododecen-l-ol by reaction with diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP) in quantitative yield, while the m-isomer gives only 8% yield of the same alcohol. Furthermore, this reagent enables us to perform the stereospecific isomerization of trisubstituted oxiranes: t-3-butyl-2-methyl-r-2-pentyloxirane is transformed into 2-pentyl-l-hepten-3-ol and the diastereomeric oxirane into (E)-6-methyl-6-undecen-5-ol, respectively. Such a rigorous stereospecificity is rationalized on the basis of a concerted syn elimination via the boat-like six membered ring imtermediary stage, in which the substituents of the oxirane ring should be arranged so as to minimize the severe nonbonded interactions.