BRIDGED TO FUSED-RING INTERCHANGE - METHODOLOGY FOR THE CONSTRUCTION OF FUSED CYCLOHEPTANES AND CYCLOOCTANES - TOTAL SYNTHESES OF LEDOL, LEDENE, AND COMPRESSANOLIDE

The type two intramolecular Diels-Alder reaction (T2IMDA) is an effici ent method for the formation of medium rings. The methodology is parti cularly effective for the construction of seven- and eight-membered ri ngs. A strategy for the synthesis of functionalized cycloheptanes and cyclooctanes has been developed that involves a bridged to fused ring interchange. The T2IMDA provides a synthesis for rigid bridged bicycli c molecules that can be stereoselectively elaborated before ozonolysis of the bridgehead double bond. Following oxidative cleavage, aldol co ndensation provides fused bicyclic ring systems that otherwise are dif ficult to synthesize. This methodology is amenable to the synthesis of terpene natural products. This is demonstrated here through total syn theses of (+/-)-ledene and (+/-)-ledene and a formal synthesis of (+/- )-compressanolide.