Abstract: Compounds are disclosed of formula (I) ##STR1## wherein R.sub.1 represents hydroxy, C.sub.1-6 alkyl, C.sub.1-6 hydroxyalkyl, C.sub.1-6 carboxyalkyl, phenyl, oxo, amino, carboxy, amido, --NR.sub.4 COR.sub.5 (where R.sub.4 and R.sub.5 both represent C.sub.1-6 alkyl), optionally substituted methylidene or, together with the carbon atom to which it is attached, R.sub.1 forms a 5 or 6-membered ring containing one or more heteroatoms;R.sub.2 and R.sub.3 are the same or different and are C.sub.1-6 alkyl or C.sub.3-6 alkenyl; or --NR.sub.2 R.sub.3 forms a 5-membered (optionally containing an oxygen atom adjacent to the nitrogen) or a 6-membered ring, which ring optionally contains one unit of unsaturation and which is unsubstituted or substituted by hydroxy, oxo, optionally substituted methylidene, --COR.sub.6 (where R.sub.6 represents C.sub.1-6 alkyl, OR, or --NHR, and R represents hydrogen, C.sub.1-6 alkyl, aryl, ar(C.sub.1-6)alkyl) or .dbd.NOR.sub.8 (where R.sub.8 represents C.sub.

Abstract: A process is described for the preparation of a compound of formula (2) ##STR1## (wherein R is a C.sub.1-6 alkyl or a C.sub.7-20 aralkyl group) and the salts thereof, which comprises reducing a compound of formula (3) ##STR2## (or a salt thereof), using a reducing system comprising borohydride ions and metal ions selected from lanthanide ions, alkaline earth metal ions or yttrium ions in solution. The reduction system may be provided by a borohydride (e.g. NaBH.sub.4) and a metal salt (e.g. CeCl.sub.3).The ester (2) may then if desired be hydrolyzed to give the parent acid.

Abstract: The present invention relates to the use of telluroxides as mild and selective oxidizing agents serving to oxidize certain functions, notably >C.dbd.S groups, in the presence of other relatively easily oxidized functions which remain unaffected; telluroxides of interest as oxidizing agents include, for example, compounds of the formula: ##STR1## wherein R and R.sup.1, which may be the same or different, each represent an optionally substituted aryl or heterocyclic group; or R and R.sup.1 together with the tellurium atom therebetween represent a heterocyclic ring, which may contain one or more further heteroatoms, and which may carry substituents and/or fused aromatic rings.