Chandra, K.G., Samita, B. and Amarendra, P. (1997) Unusual con-densation of 2-(2-dimethylaminovinyl)-1-benzopyran- 4-one with dimethyl acetylenedicarboxylate: Formation of 2,3-bis(methoxycarbonyl)xanthen-9-one. Journal of the Chemical Society, Perkin Transactions, 15, 2167-2168.