Diastereoselective, silver(I)-catalysed cyclisations of acetylenic isoureas to oxazolidines and oxazines; acetic acid-induced conversion of the alkylideneoxazines into 2-N-substituted (1Z,3E)-1,3-dienes
Abstract
O-Acetylenic isoureas R1CC[CH2]nCHR2OC(=NPri)NHPri(n= 0 or 1, e.g. R1= Me, R2= H) undergo diastereoselective, AgI-catalysed cyclisation to oxazolidines (n= 0) or oxazines (n= 1); the latter are converted into 2-N-substituted (1Z,3E)-1,3-dienes on treatment with acetic acid.