Formation of Acetylenes by Ring-Opening of 1,1,2-Trihalocyclopropanes

Abstract

This review describes studies into the conversion of substituted 1,1,2-trihalocyclopropanes into acetylenic acetals and acetylenic ketals by application of alcohols or alkoxides under basic conditions. The acetal/ketal ratio turned out to depend both on the substituents attached to the ring and on the reaction conditions prevailing during the reaction. Under the right conditions, however, completely regioselective ringopening occurs to give either acetylenic acetals or acetylenic [a] . His main research interest is synthetic chemistry, with particular emphasis on the application of cyclopropanes as starting materials and photochemical transformations as a means to incorporate particular structural features into molecules with regiochemical and stereochemical control. He is also involved in studies of oxidation reactions; these are applied to investigation of the degradation of anthropogenic organic compounds in the laboratory as well as under natural conditions in the marine environment.MICROREVIEWS: This feature introduces the readers to the authors' research through a concise overview of the selected topic. Reference to important work from others in the field is included. 3511ketals, with formation of either no or only minor amounts of other products. The reactions are thought to involve cyclopropene intermediates, which are consumed by nucleophilic attack of alcohol or alkoxide. In some cases, the cyclopropene intermediates rearrange to the corresponding vinyl carbenes, which undergo insertion reactions with protic species present in the reaction mixture and give various 2-propenal derivatives as by-products.

Syntheses ofgem-Dihalocyclopropanes and Their Use in Organic Synthesis

“…119 A possible mechanism for the formation of these products is presented in Scheme 11. 119,410 The corresponding products are formed from 1,1,2tribromo-3-methylcyclopropane in the same yield and proportion.…”

“…Substituted 1,1,2-trihalocyclopropanes transform into acetylenic alkyl acetals and/or acetylenic alkyl ketals under the conditions described . A possible mechanism for the formation of these products is presented in Scheme . ,

11

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“…Recently Sydnes has shown that 1,1,2-trihalocyclopropanes treated with concentrated aqueous NaOH and an excess of alcohol in the presence of a catalytic amount of a quaternary ammonium salt, i.e., under PTC conditions, undergo various transformations which are believed to occur through the initial formation of a gem -dihalocyclopropene by dehydrohalogenation (for a review, see ref ). It would appear that it is the quat salt of the alkoxide, and not NaOH or sodium alkoxide, which acts as a very strong base under these conditions 411 to deprotonate the substrate, as long as the substrate does not contain an electron-withdrawing or phenyl group.…”

Formation of an Isomeric Mixture of Dienynes Instead of a Diallene

“…Since the synthesis of 3,3,4,4-tetraethoxybutyne (TEB) was reported some 15 years ago [1][2][3], many of its chemical properties have been uncovered and used to prepare a range of chemical compounds with rich structural diversity [4][5][6][7][8][9][10][11][12][13][14][15]. Among the most densely functionalized molecules made is 1,1,2,2,7,7,8,8-octaethoxyocta-3,5-diyne (1), which has one ketal moiety in propargylic position to each of the triple bonds [16]. The compound therefore belongs to a group of compounds that can undergo S N 2 reactions by nucleophilic attack of the triple bond, which is accompanied by C-C bond migration that leads to the release of a leaving group from the propargylic carbon and formation of an allene moiety.…”

Novel addition reactions of titanacycle phosphonates by tuning of Ti(O-i-Pr)4/2i-PrMgClElectronic supplementary information (ESI): further experimental details. See http://www.rsc.org/suppdata/cc/b2/b209149f/

“…A possible mechanism involves attack by the Grignard on an intermediate cyclopropene oxide. 21 The sequence is equivalent to syn addition of a Grignard followed by an aldehyde. 22 The reaction takes a somewhat different course when a Cu(I) catalyst (10 mol%) is added, followed by an acyl chloride.…”