Generation and cycloadditions of 4,5-dihydrooxazole- and oxazolidine-4-carbonitrile N-oxides

Abstract

A route to 2-phenyl-4,5-dihydrooxazole-4-carbonitrile N-oxide 7 has been developed starting from (S)-serine methyl ester and involving dehydration of the 4-nitromethyl derivative 13 using m-tolylene diisocyanate and triethylamine. Cycloaddition of the nitrile oxide to styrene afforded a 55:45 mixture of diastereoisomeric dihydroisoxazoles 21 and 22; furazan N-oxides 19 and 20 were also formed in a competing dimerisation. The analogous (R)-oxazolidine-4-carbonitrile oxide 8, also prepared from (S)-serine methyl ester, reacted similarly with styrene, oct-1-ene and diethyl fumarate to afford ca. 1:1 mixtures of adducts. The structures of the dihydrooxazole–dihydroisoxazole adduct 21 and furazan N-oxide 20 were determined by X-ray crystallography.