Annulated Isoxazoles via [3+2] Cycloaddition of Alkenyl Bromides and Oximoyl Chlorides and Ag(I) Promoted Elimination

Substituted salicylaldehydes are converted to fused tetracyclic isoxazoles through a synthetic sequence incorporating substitution of 2-bromo-2-cyclohexen-1-ol, formation of an oxime function, conversion to an oximoyl chloride, intramolecular {[}3 + 2] cycloaddition, and elimination of an equivalent of hydrogen bromide using silver(I) carbonate. Six examples of this sequence are presented.