SmI2-induced reductive cyclization of (E)- and (Z)-β-alkoxyvinyl sulfones with aldehyde

SmI₂-induced reductive cyclization of (E)- and (Z)-β-alkoxyvinyl sulfones with aldehyde stereoselectively afforded 2,6-syn-2,3-trans- and 2,6-syn-2,3-cis-tetrahydropyrans, respectively. The product having a sulfonylmethyl group was converted to a cyclic ether having a methyl group by reduction with Raney-Ni.     

Synthetic study of gymnocin-A: synthesis of the ABC ring fragment

The synthesis of the ABC ring fragment of gymnocin-A is described. The key feature of this approach was the convergent BC ring formation using an oxiranyl anion coupling, which was followed by intramolecular Williamson ether synthesis and the reductive etherification of an α-acetoxy acetal. The five-membered A ring was then constructed on the seven-membered B ring by radical cyclization of a β-alkoxy acrylate derivative.