A Diadtereoselective Synthesis of threo 2-(a-Hydroxyalkyl)piperdines via Oxacarbamoylinium Ion-(Z)-vinylsilane Cyclization

Abstract

3 -b u t e n y l )oxazolidine-2,4diones (2) w i t h NaBH4, f o l l o w e d by c y c l i z a t i o n w i t h TiC14 afforded t h e corresponding 1 , 8 a -~-l -a l k y l -1 , 5 , 6 , 8 a -t e t r a h y d r o -3 ~-o x a z o l o [ 3 , 4 -a ] p y r idines (9a,b), r e s p e c t i v e l y , w i t h h i g h d i a s t e r e o s e l e c t i v i t y .C a t a l y t i c hydrogenation o f 5, f o l l o w e d by a l k a l i n e h y d r o l y s i s gave three ?-( ah y d r o x y e t h y 1 ) p i p e r i d i n e (&).I n a s i m i l a r fashion, -2-(a-hydroxyp r o p y 1 ) p i p e r i d i n e (El, (A)-5-conhydrine, was obtained from x.