Radical Cyclization Strategies To Bridged Systems - Regioselective Construction Of Chiral Bicyclo [2.2.2] And [3.2.1] Octanes Via 6-Exo Trig And 5-Exo Trig Radical Cyclization Reactions

Radical cyclisation reaction of the bromoenones 6 and 7, obtained from (R)-phenylcarvone 3, gave a mixture of bicyclo [2.2.2] and [3.2.1] octanones via competitive 6-exo trig and 5-exo trig modes. On the other hand, radical cyclisation reaction of the alcohol 12 furnished the bicyclo[3.2.1]-octanol 15 as the major cyclised product, where as the alcohol 13 furnished the bicyclo[2.2.2]octanol 18 as the major cyclised product. An explanation based on conformational rigidity due to the intramolecular hydrogen bonding between the hydroxy and methoxy groups is proposed, and proved by the formation of bicyclo[2.2.2]octanes as major cyclised products with the corresponding acetates 19 and 20.