or alkoxy aryloxy alkylaryloxy arylalkoxy preferably methoxy ethoxy or u2014 o u2212 me wherein me is alkali or earth alkali metal cation preferably li na k mg ca or ba wherein r 3 is a metal containing group especially an alkali or earth alkali metallic radical as lithium sodium potassium or a group of formula mg halogen grignard reagent u2014 znhalogen cer halogen 2 or boronic acid as u2014 b oh 2 but preferably u2014 li or u2014 mgbr or mgate complex in inert organic solvent preferably thf followed by reaction with a reagent lvg c u2550 o lvg wherein lvg is a suitable leaving group preferably reagent such as phosgene clcocl di or tri phosgene clc u2550 o occl 3 or cl 3 coc u2550 o occcl 3 or n n carbonyl diimidazole or alkyl or aryl chloroformate such as clc u2550 o oalkyl clc u2550 o oaryl cl u2550 o coalkylaryl clc u2550 o oarylalkyl wherein r 4 and x u2212 are the same as defined for compound of formula i compound of formula iii can be any oxalic acid derivative preferably oxalic acid itself or oxalic acid diester with lower alkyl aryl or arylalkyl ester group or a half ester containing lower alkyl or aryl or arylalkyl ester group wherein the carboxylic acid function could be either a free acid or a salt thereof with alkali or earth alkali metal cation or an ammonium.