Abstract: The invention relates to novel monoesters and diesters of 9,10-endoethano-9,10-dihydroanthracene-11,11-dicarboxylic acid.These novel monoesters and diesters correspond to the following structural chemical formula (II): ##STR1## in which R.sup.1 and R.sup.2 are identical or different and can represent H, an alkali metal or alkaline earth metal atom, a linear or branched alkyl group having from 1 to 6 carbon atoms, an alicyclic group having form 3 to 6 carbon atoms, an alkenyl group having from 2 to 6 carbon atoms, defined in their cis or trans variety, or an alkynyl group having from 2 to 6 carbon atoms, the said groups optionally being substituted by one or more functional groups such as ether, epoxide, halogeno, cyano, ester, aldehyde, ketone, aryl etc., where R.sup.1 and R.sup.2 cannot be H or ethyl simultaneously. These addition products constitute valuable intermediates for the preparation of methylidenemalonates in high yields and with a high purity.

Abstract: The invention relates to novel monoesters and diesters of 9,10-endoethano-9,10-dihydroanthracene-11,11-dicarboxylic acid.These novel monoesters and diesters correspond to the following structural chemical formula (II): ##STR1## in which R.sup.1 and R.sup.2 are identical or different and can represent H, an alkali metal or alkaline earth metal atom, a linear or branched alkyl group having from 1 to 6 carbon atoms, an alicyclic group having from 3 to 6 carbon atoms, an alkenyl group having from 2 to 6 carbon atoms, defined in their cis or trans variety, or an alkynyl group having from 2 to 6 carbon atoms, the said groups optionally being substituted by one or more functional groups such as ether, epoxide, halogeno, cyano, ester, aldehyde, ketone, aryl etc., where R.sup.1 and R.sup.2 cannot be H or ethyl simultaneously. These addition products constitute valuable intermediates for the preparation of methylidenemalonates in high yields and with a high purity.