The reactions of β-thevinone and β-dihydrothevinone with tert- butylmagnesium chloride and n-propylmagnesium bromide were investigated. Further chemical transformations (N-demethylation, N-alkylation, O- demethylation) of the tertiary alcohols afforded the known β-buprenorphine and the hitherto unknown β-etorphine and β-dihydroetorphine. The by- products of these reactions were also isolated, their structures identified, and the mode of their formation was explained.