Carbonylierende Ringerweiterung, 5. Enantioselektive Synthese des Bicyclo[3.2.1]oct‐3‐en‐2,8‐dion‐Systems durch doppelte Carbonylierung von α‐Terpinen und anderen prochiralen Cyclohexadienen

Abstract

Carbonylating Ring Enlargement, 51). – Enantioselective Synthesis of the Bicyclo[3.2.l]oct‐3‐ene‐2,8‐dione Systems by Double Carbonylation of α‐Terpinene and Other Prochiral CyclohexadienesThe steric information in tricarbonyl iron complexes of type 2(R1 ≠ R2), established during the complexation of prochiral 1,3‐cyclohexadienes can be transferred to bicyclo[3.2.1]oct‐3‐ene‐2,8‐diones by metal‐induced ring enlargement and bridging carbonylation. This was verified by the synthesis and conversion of optically active tricarbonyl iron complexes 2 of α‐terpinene (1). These complexes can be either obtained by chirality transfer during complexation and rearrangement of (R)‐(+)‐ or (S)‐(‐)‐limonene (7) or by separation of racemic mixtures on triacetyl cellulose. The separation on chiral phases and subsequent stereoselective conversion to bicyclo[3.2.1]oct‐3‐ene‐2,8‐diones may also be carried out with other tricarbonyl iron complexes of prochiral cyclohexadienes (lacking additional functional groups).