Process for preparing 1,2-oxa-phospholanes

Process for preparing 2,5-dioxo-1,2-oxa-phospholanes having general formula (I) ##STR9## wherein R.sup.1 represents an alkyl group or a substituted alkyl group having up to 18 carbon atoms, a cycloalkyl group having up to 8 carbon atoms, an alkenyl group having up to 8 carbon atoms, an aryl group having up to 14 carbon atoms, which may be substituted by lower alkyl groups having up to 4 carbon atoms, by lower alkoxy groups having up to 4 carbon atoms, halogen or by amino groups alkylated or dialkylated by lower alkyl radicals having up to 4 carbon atoms, or an aralkyl group having up to 15 carbon atoms and which may be substituted in the same way as the aryl group, wherein

• R.sup.2 stands for an alkyl group having up to 4 carbon atoms, or hydrogen and wherein
• R.sup.3 stands for an alkyl radical having up to 4 carbon atoms, a phenyl radical or a phenyl radical being substituted by halogen or by lower alkyl groups having up to 4 carbon atoms, for a benzyl radical or hydrogen, which comprises reacting dihalogenophosphines of general formula (II) ##STR10## wherein R.sup.1 has the same meaning as in formula (I) and wherein X stands for chlorine or bromine, with an equimolar quantity of an .alpha.,.beta.-unsaturated acid of formula (III) ##STR11## wherein R.sup.2 and R.sup.3 have the same meaning as in formula (I), and simultaneously, with an equivalent quantity of a compound of formula (IV),
• r.sup.4 -- oh (iv)
• wherein R.sup.4 represents hydrogen or an acyl radical substituted by a hydroxy group in .alpha.- or .beta.-position or which may be substituted once, twice or three times by halogen, or by a carboxyl group, or wherein R.sup.4 represents the radical --CO--COOH, an alkyl-sulfonyl radical, a phenyl-sulfonyl radical, a phenalkyl-sulfonyl radical or an alkylphenyl-sulfonyl radical having up to 12 carbon atoms, or wherein R.sup.4 represents a radical of formula (IVa), ##STR12## wherein R.sup.5 represents an alkyl radical having up to 12 carbon atoms which may be substituted by halogen, a cycloalkyl radical having up to 8 carbon atoms or an alkenyl radical having from 2 to 12 carbon atoms,
• and wherein R.sup.6 has the same meaning as specified for R.sup.5 or stands for a carboxylic acid group having from 2 to 4 carbon atoms or HO(CH.sub.2).sub.3 -- or HO(CH.sub.2).sub.4 --, or with an equivalent quantity of a compound having formula (V) ##STR13## wherein R.sup.5 and R.sup.6 have the same meaning as in formula (IVa) and wherein R.sup.7 has the meaning of R.sup.5 or represents a group of formula (IVa),
• or with an equivalent quantity of mixtures of the compounds having formulae (IV) and (V) and isolating the reaction products.