When the combination of zinc triflate and chlorotrimethylsilane
is substituted for a Brønsted acid, the classic Passerini
reaction of carbonyl compounds with t-butyl
isonitrile affords an efficient 1:2 condensation product leading
to β-hydroxy-α-cyanoenamines 17a-f,
which can be transformed into 5-substituted-4-cyanooxazoles 8a-f in
one step. In contrast to the corresponding Ti-mediated condensations
of carbonyl compounds with t-butyl isonitrile,
no cyanohydrins are formed.
oxazole - Passerini - condensation - isonitrile - combinatorial chemistry