Hetero Diels-Alder reactions of 2-chloro-1-nitroso-1-phenylethene: Preparation of novel 4-chloro-substituted 1,2-oxazines and subsequent reactions

摘要

The cycloaddition of 2-chloro-1-nitroso-1-phenylethene (3), generated in situ from 2,2-dichloro-1-phenylethan-1-one oxime (2) to electron-rich olefins, e.g. silyl enol ethers or alkyl enol ethers, furnished the 4-chloro-substituted 5,6-dihydro-4H-1,2-oxazines and 6H-1,2-oxazines in moderate to good yields and with good diastereoselectivities. Bromo enol ether 18 led to the unexpected alpha,alpha-dichloro oxime derivative 21 as well as the halogenated 6H-1,2-oxazines 19 and 20. Starting from 4-chloro-1,2-oxazines 5 and 17, 4-azido-, 4-amino-, 4-hydroxy-, and 4-oxo-substituted 1,2-oxazines were prepared. Hydrogenolysis of 5,6-dihydro-4H-1,2-oxazine 5 afforded amine 31.