Synthesis of diacetal trioxa-cage compounds via a sequential cyclization reaction of norbornene derivatives induced by electrophiles

Abstract

The synthesis of diacetal trioxa-cage compounds via a sequential cyclization reaction of norbornene derivatives induced by electrophiles in a short sequence is reported. Treatment of the norbornene derivatives 2a-d and 10b with I-2 in aqueous THF in the presence of KI at 25 degrees C regioselectively gave the iodo-cage compounds 3a-d and 11 in 80-90% yields, respectively, via a iodine-induced sequential cyclization reaction. No detectable amount of other regioisomers or monocyclization products was obtained. The synthesis of triora-cages 14a-e was accomplished from 3a-d and 11 in a two-step sequence. Treatment of diacylnorbornenes 15a-f with I-2 in aqueous THF at 25 degrees C regioselectively and stereoselectively gave the sequential cyclization products 16a-f, respectively, which were converted in one step to the diacetal trioxa-cages 24a-f in high yields. The structure of these trioxa-cages was proven by X-ray analysis of the crystalline compound 14e. Other electrophiles, such as bromine, m-CPBA, and Hg(OAc)(2), were also found to be effective for the sequential cyclization reaction. Oxymercuration of 15a-f and 2a-c with Hg(OAc)(2) in aqueous THF followed by reduction with NaBH4 at 25 degrees C gave compounds 28a-f and 30b,d,c in high yields, respectively.