Glycals allyl

It was envisaged that the enones were produced following abstraction of H-1 (a process facilitated by the ability of sulfur atoms to stabilize radicals on bonded carbon centers), radical bromination, elimination of hydrogen bromide to give substituted glycals, allylic bromination at C-3, and loss of acetyl bromide. In the formation of compound 6, hydrogen abstraction from C-5 was deemed to compete with that from C-1, and to lead to substitution at the former site with the formation of a relatively stable product. 

TABLE 37.4. Ferrier Rearrangement of Glycal Allylic Ethers... 

Perrier RJ (2001) Substitution-with-Allylic-Rearrangement Reactions of Glycal Derivatives. 215 153-175... 

Tochtermann reported the addition of dichlorocarbene to the racemic glycal 52, whose cyclopropyl-allyl rearrangement leads to the 2//-pyran. The synthesis of the optically pure (+)-(2S,3R,7S) and (-)-(2f ,3S,7f )-glycal precursors has also been achieved. As pointed out, optically pure glycals are versatile precursors for carbohydrate synthesis <00EJO1741>. 

Scheme 5.62 Conjugate addition to allylic aziridines in glycals.

C-Allyl glycosides can be prepared by the reaction of glycal epoxides with allyltributyltin in the presence of tributyltin triflate as a Lewis acid,281 and aldonitrones can be allylated with trimethylsilyl triflate as a catalyst (Equations (101) and (102)).282... 

---