General Method for Synthesizing Pyranoid Glycals. A New Route to Allal and Gulal Derivatives

Pyranoid glycals of all configurations can be obtained from pentoses through an olefination−cyclization−elimination sequence. The elimination can be carried out with excellent yields under radical conditions or by using common reductive reagents such as Zn/Cu, TiCl₄/LiAlH₄, or lithium naphthalenide. The proposed method is appropriate for the synthesis of glycals with allo or gulo configurations because the cyclization step is more efficient for these substrates.