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The action of 2-(1-arylethylidene)malononitriles on 2-nitro-1H-benzofchromenes in the presence of Et3N and MoO3·2H2O results in naphtho2,1-bfurans containing an allylidenemalononitrile unit in the α-position. The reaction proceeds with contraction of the pyran ring via a cascade carba-Michael addition/retro-oxa-Michael reaction/tautomerization/SN2/oxidation process. In contrast, the reaction of 2-nitro-1H-benzofchromenes with the cyclic Knoevenagel adduct derived from 1-indanone and malononitrile leads to dihydroindeno1,2-cxanthenes. The possibility of further transformations of naphtho2,1-bfuran derivatives as useful precursors and their optical properties were also investigated.
Корженко et al. (Thu,) studied this question.