Synthesis of chiral tricyclo[3.2.1.02,7]octanes by an efficient 3-exo-trig radical cyclisation reaction1

Abstract

Synthesis of chiral tricyclo[3.2.1.0^2,7]octanes by efficient and exclusive 3-exo-trig radical cyclisation of either a bicyclo[3.2.1]oct-6-en-2-yl radical or a bicyclo[2.2.2]oct-5-en-2-yl radical is described. Reaction of the methoxy enones 7a–c with boron tribromide at low temperature furnishes the bicyclo[3.2.1]octenyl bromides 9a–c and 10a–c along with varying amounts of 8a–c, whereas the methoxy enone 7d provides the unrearranged bicyclo[2.2.2]octenyl bromide 8d. Treatment of the homoallyl bromides 9a–c and 10a–c and 8d with tributyltin hydride and AIBN generates, exclusively, the tricyclic ketones 15a–d.