RING TRANSFORMATIONS OF PHOSPHORUS-CONTAINING HETEROCYCLES .10. CONVENIENT SYNTHESIS OF 1-ALKOXY-DIHYDROPHOSPHININE AND TETRAHYDROPHOSPHININE 1-OXIDES BY RING ENLARGEMENT

Double bond of the P-alkoxy 3,4-dimethyl-3-phospholene-1-oxides reacts easily with dichlorocarbene to give two diastereomers of an unstable adduct useful int he synthesis of ring-expanded products, such as 1,2-dihydrophosphinine-oxides or 1,2,3,6-tetrahydrophosphinine-oxides. The former can be prepared by thermolysis of the adducts, while the latter are obtained by cyclopropane ring opening effected by silver nitrate in a protic solvent. Preparation of the double bond isomers of 1-alkoxy-tetrahydrophosphinine-oxides containing only methyl substituent in the ring is also described. The reaction of the 3-phospholene-oxides with dichlorocarbene can be modified to give P-alkoxy 1,4-dihydrophosphinine-oxides in an unexpected reaction.