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Carbonyl ylides arising from ethyl acetodiazoacetate/dimethyl diazomalonate and α,β‐enones with mainly s‐cis conformations underwent disrotatory cyclization to produce dihydrofuran derivatives. This process proved to be sensitive to steric effects. The corresponding ylides arising from rather s‐trans α,β‐enals yielded dioxole derivatives. The mechanisms of the reactions are discussed.

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(15.XI. 95)Ten new a -diazo$-oxoaldehydes were condensed with aniline, ammonia, hydroxylamine, and semicarbazide to yield new 4-acyl-(l-substituted)-l H-l,2,3-triazoles in moderate-to-good yields. The method is simple and regiospecific. The latter feature makes this method superior to the widely used acylacetyiene + azide approach.

~ ~~~Several cyclic and acyclic enones and their ethylene ketals/acetals were reacted with dimethyl diazomalonate under bis(acetylacetonato)copper(II) catalysis. Cyclohex-2-en-I-one (1) yielded only C-H insertion products 2 and 3, whereas but-3-en-2-one gave a cyclopropane albeit in very low yield. The ethylene ketals 6 of cyclopent-2-en-I-one and cyclohex-2-en-I-one gave the corresponding cyclopropanes 7, which were in turn cleaved to the ketones 8. The acetals 9 and 10 of crotonaldehyde ((E)-but-2-enal) and cinnamaldehyde ((E)-3-phenylprop-2-enal), respectively, yielded C-0 insertion and [2,3]-sigmatropic rearrangement products l l b , c and 12b, c, as well as cyclopropanes l l a and l l b , all of which are polyfunctional and synthetically useful compounds.