Carbohydrate Spiro-heterocycles via Radical Chemistry

Abstract

This review summarizes the current status of the preparation of spiro-heterocycles fused with a pyranose or furanose carbohydrate skeleton, using free radical chemistry. A variety of heterospiro[m.n]alkane bicyclic structures (m = 3–5, n = 4–6) possessing one, two, or three heteroatoms (N, O, Si, S) have been collected, in addition to three different 1,6,8-trioxadispiro-tetradecane and 1,6,8-trioxadispiro-pentadecane tricyclic systems. C(sp3)–H bond functionalization by 1,5- or 1,6-hydrogen atom transfer (HAT) initiated by C(sp3)-, C(sp2)-, O-, or N-radicals and 5-exo-trig or 6-exo-trig cyclization reactions are the most useful strategies employed for the construction of the heterocyclic rings. The intramolecular HAT promoted by photoexcited monoketones, α-diketones, furanones, and succinimides via a Norrish type II–Yang cyclization process has also been successfully applied.