Synthesis of Rings with One Oxygen Atom

Vinylcarbene, generated by photolysis of substituted pyrazolenine, affords a mixture of the cyclopropene derivative and vinyloxirane 200 via insertion into an a-hydroxy group [66JCS(C)1719]. Phenyloxiranes 

Oxiranes 201 have been obtained in 66-79% yields as an equimolar mixture of cis and trans isomers in the reaction of alkoxide anions with phenylchlorocarbene generated from benzal chloride and potassium tert-butoxide (83JA2771). 

and 207 with complete enantioselectivity from optically active amino alcohols (82H209 90TL4573) or esters of amino acids (84TL1205). 

Photolytic and catalytic decomposition of a-diazo esters produces )8-lactones, which are formed via intramolecular C—H insertion of a carbene or carbenoids. Tertiary alkyl esters of diazomalonic acid are decomposed by rhodium acetate with exclusive formation of the four-membered ring 211. This suggests a smooth insertion into the C—H bond activated by the adjacent oxygen atom (90TL1023). jS-Lactone 212 was obtained by photolysis of diazo malonic ester 213 (71CC577). 

Benzoxetanes 214 were observed among the photolysis products of diar-yldiazomethanes containing an ortho hydroxy group [91JCS(P1)471], Substituted oxetane carboxylic acid 215 was first synthesized in preparative 

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