(Ar= p-MeOC&) acetonitrile under the DCA-sensitized conditions la and lb gave 3ai2 and 3bi2 in 6% and 72% yields, respectively. The yield of 3a was increased to 48% by the addition of Mg (C104) 2.13 If the initial cyclization occurs in a stereospecific manner, its stereochemical integrity should be conserved in the oxygenation product. In order to test this, the direct molecular oxygen trapping of intermediates was further applied for (2, Z)-,(E ...
