Highly functionalized cyclopentanes by radical cyclization of unsaturated bromolactones. 2. A facile synthesis of the first carbaaldohexofuranoses and their conversion to carbapentofuranoses

A novel type of carbasugars, carbaaldohexofuranoses, has been prepared using a 5-exo-trig radical cyclization of C-2 substituted 2,3-unsaturated 7-bromoheptono-1,4-lactones as the key step. During the cyclization step, two-stereogenic centers were farmed with high stereoselectivity. The lactone moieties of the cyclopentane derivatives were reduced to the alcohols, and the following carbahexofuranoses were synthesized: carba-beta-D-mannofuranose, carba-alpha-L-glucofuranose and 5-amino-5-deoxycarba-alpha-L-glucofuranose. Side chain degradation of the two former compounds gave the carbapentofuranoses: carba-alpha-L-xylofuranose and carba-beta-D-lyxofuranose.