N,O-Nucleosides from Ene Reactions of Nitrosocarbonyl Intermediates with the 3-Methyl-2-buten-1-ol

Nitrosocarbonyl intermediates undergo ene reactions with allylic alcohols, affording regioisomeric adducts in fair yields. Nitrosocarbonyl benzene reacts with 3-methyl-2-buten-1-ol and follows a Markovnikov orientation and abstracts preferentially the twix hydrogens over the lone ones. With the more sterically demanding nitrosocarbonyl mesitylene and anthracene, the Markovnikov directing effect is relieved and lone abstraction is observed, affording the 5-hydroxy-isoxazolidines that serve as synthons for the preparation of N,O-nucleoside analogues according to the Vorbruggen protocol.