Compounds of the formula (I) ##STR1## (in which X represents HS-- or a group R.sub.1 R.sub.2 N-- wherein R.sub.1 and R.sub.2 which may be the same or different represent hydrogen or a straight or branched chain alkyl group containing from 1 to 4 carbon atoms or a benzyl group and R.sub.3 represents a C.sub.3-7 alkyl group or a C.sub.3-7 cycloalkyl group) are prepared by reacting an .alpha.-ketoester of the formula (II) ##STR2## (in which Alk represents an alkyl group) or a precursor thereof with a compound of the formula (III) ##STR3## The precursor of the compound of formula (II) may be a mixture of isomeric enol esters ##STR4## The compounds of formula (I) may be converted into compounds of formula VIII ##STR5## in which R.sub.1 and R.sub.2 which may be the same or different represent hydrogen or a straight or branched chain alkyl group containing from 1 to 4 carbon atoms, and R.sub.3 is as defined above.
化合物的公式为(I) ##STR1## 其中X代表HS--或R.sub.1 R.sub.2 N--基团,其中R.sub.1和R.sub.2可以相同或不同,代表氢或1至4个碳原子的直链或支链烷基或苄基,而R.sub.3代表C.sub.3-7烷基或C.sub.3-7环烷基。这些化合物可以通过将公式(II) ##STR2##(其中Alk代表烷基)的α-
酮酯或其前体与公式(III) ##STR3##的化合物反应而制备得到。化合物公式(II)的前体可以是异构的烯醇酯混合物 ##STR4##。公式(I)的化合物可以转化为公式VIII的化合物 ##STR5## 其中R.sub.1和R.sub.2可以相同或不同,代表氢或1至4个碳原子的直链或支链烷基,而R.sub.3如上所定义。