Carbonylierende Ringerweiterung, 4. Diastereoselektive Synthesen von Bicyclo[3.2.1]oct‐3‐en‐2,8‐dionen durch doppelte Carbonylierung von (R)‐(‐)‐α‐Phellandren

Carbonylating Ring Enlargement, 41). – Diastereoselective Syntheses of Bicyclo[3.2.l]oct‐3‐ene‐2,8‐diones by Double Carbonylation of (It)‐(‐)‐α‐Phellandrene In order to clarify the stereochemistry of the carbonylating ring enlargement of cyclohexadiene complexes 1 to complexed seven‐membered ring ketones 2 and the further carbonylation to bicyclo[3.2.1]oct‐3‐ene‐2,8‐diones 3 the exo and endo isomers of (R)‐(‐)‐α‐phellandrene complex 7 were synthesized in pure form and in various isomeric ratios and converted. The optically active ring‐enlargement products 11 and 12 obtained therefrom, as well as the enantiomerically pure bicyclooctenes 20–22, implicate a stereospecific reaction course under retention of the configuration predetermined by the starting material 6 and its complexes 7. This was confirmed by an X‐ray determination of the absolute configuration of exo‐12. Thus, the method is suitable for the diastereoselective synthesis of bicyclo[3.2.1]oct‐3‐ene‐2,8‐diones 3 from 1,3‐cyclohexadiene complexes 1.