Highly Functionalised Cyclopentanes by Radical Cyclisation of Unsaturated Bromolactones II. 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 cyclisation of C-2 substituted 2,3-unsaturated 7-bromoheptono-1,4-lactones as the key step. During the cyclisation step two stereogenic centres were formed with high stereoselectivity. The lactone moieties of the cyclopentane derivatives were reduced to the alcohols, and the following carbahexofuranoses were synthesised: carba--D-mannofuranose, carba--L-glucofuranose and 5-amino-5-deoxycarba--L-glucofuranose. Side chain degradation of the two former compounds gave the carbapentofuranoses: carba--L-xylofuranose and carba--D-lyxofuranose.