Radical cyclization reaction of α-bromo-α-acyloxy-ω-unsaturated alkanes

Abstract

Radical cyclization reactions developed in the last few years represent a breakthrough for synthetic radical chemistry. These reactions exhibit interesting regioselectivities and stereoselectivities and can be carried out with a variety of functional groups. The placement of a variety of radical stabilizing groups Y at radical center may slow the cyclization, and can promote competing formation of 6-endo and uncyclized reduced products. $\alpha$ -Bromo-$\alpha$ -acyloxy-$\omega$ -unsaturated alkanes give good yield of the exo-products. The radical is slowly cyclized because the acetate substituent is an electron-withdrawing group. The results of this experiment showed regioselectivity for 5-and 6-exo cyclization which proves the stabilizing effects of acetate was not sufficient for 63 and 65 to be reversible. Reverse stereoselectivity or $\alpha$ -Bromo-$\alpha$ -acyloxy-$\omega$ -unsaturated alkanes was proved that charge repulsion between partial negative charge at oxygen and the developing radical center should disfavor formation of the cis-products.