CARBONYLATING RING ENLARGEMENT .3. STEREOCHEMISTRY OF COMPLEXATION AND CARBONYLATING RING ENLARGEMENT OF 1,3,5-TRIMETHYL-1,3-CYCLOHEXADIENE

Carbonylating Ring Enlargement, 31). – Stereochemistry of Complexation and Carbonylating Ring Enlargement of 1,3,5‐Trimethyl‐1,3‐cyclohexadiene The stereochemical course of the complexation and the metal‐ and Lewis acid induced carbonylating ring enlargement of cyclohexadienes 1 to bicyclo[3.2.1]oct‐3‐ene‐2,8‐diones 4 via diene iron tricarbonyl complexes 2 and complexed sevenmembered ring ketones 3 is investigated by synthesis and conversion of the diastereomeric complexes exo‐ and endo‐12 of 1,3,5‐trimethyl‐1,3‐cyclohexadiene (7). It can be concluded, that the stereochemical information of the starting materials can be transferred to the product. In the first step exo and endo substituents retain their relative position towards the metal. The introduction of the second carbon monoxide unit and ketone bridge formation also occurs stereospecifically from the side of the complexing metal without loosing the preestablished position of the substituents. Mechanistic aspects of these results are discussed. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim