Radical cyclisation of some 1,2,6-trideoxy-3,4-di-O-benzyl-6-halogeno-l-arabino-hex-1-ynitol derivatives

Free radical cyclisation of the title halides 5a, 5b, 5c and 16 led to five-membered carbocycles in good yield. The main products are two isomeric deoxy compounds resulting from the extrusion of benzaldehyde. A three-step process [5-exo-digcyclisation, 1,5 hydrogen-atom-transfer, fragmentation] is proposed to explain their formation.