2,3-Dibromo-3-phenylpropiophenones eliminated both bromine and hydrogen bromide on reaction with dimethyloxosulphonium methylide (DMOSM) ; the resulting ap-unsaturated ketones formed cyclopropyl ketones which, when suitably substituted, continued to react with DMOSM, forming a variety of heterocyclic products. A contiguous cyclopropyl epoxide underwent ring-opening oxymercuriation with mercuric acetate via 5-oxypent-2-en-1 -01s. A cyclopropylcyclopropane analogue of the epoxide was stable at 300 "C.
Cyclopropyl epoxides having aryl substituents in the 1 -position of the cyclopropane ring underwent acid-catalysed rearrangement to Iand 2-arylcyclobutenes ; in methanol they formed stereoisomeric 1 -aryl-I -methoxycyclobutanes. A cyclopropyl epoxide substituted in the 2-position of the cyclopropane ring by geminal methyl groups rearranged to a hexa-2.5-dien-I -01 rather than a 3.6-dihydro-2H-pyran. Except in the formation of stereoisomeric pent-2-en-I -01s. cyclopropyl epoxides unsubstituted in the alicyclic ring underwent typical epoxide reactions. THE rearrangement of oxirans having a contiguous cyclopropane ring has been the subject of recent studies. Prinzbach and Fischer proposed that the rearrangement of an oxabicyclobutane intermediate (11) best accounts for the products obtained in the reaction of a cyclopropene (I) with peracetic acid. This proposal is supported by later work.2 The oxaspiropentane system has been the subject of a detailed study.3 Its characteristic rearrangement is to form a cyclobutanone, as exemplified4 by the parent compound (111). The
Die durch Umsetzung der Ketone (I) mit Dimethylsulfoniummethylid erhältlichen isomeren Cyclopropylepoxide (II) und (III) lagern sich bei kurzem Erhitzen in einem Lösungsmittel oder in Substanz [nur (IIb)/(IIIb) reagieren langsam] oder spontan bei Raumtemperatur in Gegenwart von Spuren p‐Tolu olsulfonsäure (im Lösungsmittel) in die Dihydropyrane (IV) um.
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