Vinylation of 2,3:4,5-di-O-isopropylidene-aldehydo-D-arabinose gave a 1.3:1 mixture of 1,2:3,4-di-O-isopropylidene-6-heptene-L-gulo(andD-manno)-1,2,3,4,5-pentol (1aand2a). Successive ozonolysis and hydrolysis of the mixture of1aand2agaveD-glucose andD-mannose in a ratio of 1.4:1. Vinylation of 2,4-O-ethylidene-aldehydo-D-erythrose gave a 3.9:1 mixture of 1,3-O-ethylidene-5-hexene-L-ribo(andD-lyxo)-1,2,3,4-tetrol (3aand4a), which was degraded to formD-ribose andD-arabinose in a ratio of 4:1. The configuration of each of theC-vinyl compounds1a,2a,3a, and4awas assigned by degradation to the corresponding aldose.