Process for preparing 4,5-dihydro-4-oxofuran-2-carboxylic acid derivatives

A process for preparing a compound of formula 1 ##STR9## in which R.sup.1 and R.sup.2 each is lower alkyl, cyclo(lower)alkyl, lower alkoxy(lower)alkylene, phenyl or phenyl mono- or disubstituted with lower alkyl, lower alkoxy, halo, nitro or trifluoromethyl;

• or R.sup.1 and R.sup.2 together form a --(CH.sub.2).sub.m --X--(CH.sub.2).sub.n -- chain wherein m and n each is an integer from one to four and X is methylene, oxa or thia;
• or R.sup.1 and R.sup.2 together with the carbon atom to which they are joined form a spiro[1,2,3,4-tetrahydronaphthalene]-1 or spiro-[indan]-1 radical;
• R.sup.3 is hydrogen or lower alkyl;
• and R.sup.4 is hydrogen, lower alkyl, cyclo(lower)alkyl, phenyl(lower)alkylene, amino(lower)alkylene, lower alkylamino(lower)alkylene, di(lower)alkylamino(lower)alkylene or 3-pyridinyl(lower)alkylene, which comprises:
• reacting a compound of formula 11 ##STR10## in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein with a di(lower alkyl) oxalate in the presence of a strong inorganic proton acceptor under anhydrous conditions, hydrolyzing the mixture with water at about pH 10 to about pH 12, and allowing the latter mixture to stand under acidic conditions to obtain the compound of formula 1 in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein and R.sup.4 is hydrogen;
• and if desired,
• esterifying the latter compound of formula 1 to obtain the corresponding compound of formula 1 in which R.sup.1, R.sup.2 and R.sup.3 are as defined herein and R.sup.4 is lower alkyl, cyclo(lower)alkyl, phenyl(lower)alkylene, amino(lower)alkylene, lower alkylamino(lower)alkylene, di(lower alkyl)amino(lower)alkylene or 3-pyridinyl(lower)alkylene.