Do alpha-acyloxy and alpha-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

The generation of alpha-acyloxy and alpha-alkoxycarbonyloxy radicals under reductive conditions in fragmentable probe experiments does not provide unequivocal evidence for the fragmentation of such radicals to give ketones and acyl or alkoxycarbonyl radicals. Instead, standard reduction predominates, even at low tin hydride concentrations. Some ketone product is formed in the alpha-acyloxy substrate at low concentrations, but it is unclear whether this product arises through a slow radical fragmentation process or an inefficient, chain-breaking oxidative process.

Discodermolide/Dictyostatin hybrids: synthesis and biological evaluation.

[structure: see text] Two hybrid analogues of discodermolide and dictyostatin (3, 26) have been designed and synthesized. These are the first macrocyclic analogues of discodermolide and biological activities were evaluated and compared with linear discodermolide analogues.