Cyclopropane alkene conversion into

A very effective means for conversion of alkenes into cyclopropanes by transfer of a CH2 unit involves the system CH2I2 and Zn-Cu couple, commonly referred to as the Simmons-Smith reagent. The active species is believed to be iodomethylzinc... 

Interestingly, sulfonium ylides generated from electrophilic carbene complexes and sulfides can react with carbonyl compounds, imines, or acceptor-substituted alkenes to yield oxiranes [1320-1325], aziridines [1321,1326,1327] or cyclopropanes [1328,1329], respectively. In all these transformations the thioether used to form the sulfonium ylide is regenerated and so, catalytic amounts of thioether can be sufficient for complete conversion of a given carbene precursor into the... 

Even thiophene itself will react with carbenes, at sulfur, to produce isolable thiophenium ylides, and in these, the sulfur is definitely tetrahedral. The rearrangement of thiophenium bis(ethoxycarbonyl) methylide to the 2-substituted thiophene provides a rationalisation for the reaction of thiophene with ethyl diazoacetate, which produces what appears to be the product of carbene addition to the 2,3-double bond perhaps this proceeds via initial attack at sulfur followed by S C-2 rearrangement, then collapse to the cyclopropane. Acid catalyses conversion of the cyclopropanated compound into a thiophene-3-acetic ester. ° 2,5-Dichlorothiophenium bis(methoxycarbonyl)methylide has been used as an efficient source of the carbene simply heating it in an alkene results in the transfer of (Me02C)2C to the alkene. ... 

Cyclopropane derivatives have been prepared using alkenes, cm-dihalides, and copper. This is a convenient and useful procedure, e.g. cis-cyclo-octene was converted into bicyclo[6,l,0]nonane (77%) and into a mixture of endo- and cxo-9-methoxy-carbonylbicyclo[6,l,0]nonanes (71 % exo. endo = 1.3 1) using di-iodomethane and methyl dibromoacetate, respectively. An improved procedure for the conversion of alkenes into cyclopropanols uses lithium 2,2,6,6-tetramethylpiperidide and 2-chloroethyl chloromethyl ether, e.g. cycloheptene was converted into the 2-chloro-ethyl ether of bicyclo[5,l,0]octan-8-ol (62% exo.endo = 1.8 1). ... 

The addition of R MgBr to a-chloro-ketones gives (37) which on lithiation extrudes LiMgBrO to yield alkenes." The fact that spiroactivated cyclopropanes are susceptible to nucleophilic attack has been extended to organo-metallics, and exploited in the conversion of (38) into (39) by acetylenic Grignard addition during a synthesis of ( )-Brefeldin A. ... 

Natural Cyclopropanes.—In extensions of their earlier investigations of the synthesis of chrysanthemic acid (25) based on elaboration of the cyclopropane ring by reaction between the isopropyl ylide (22) and alkene substrates (see Volume 1, p. 292), Krief and his co-workers have now shown that the ylide (22) can be added to both maleate and fumarate, leading to the frans-cyclo-propanedicarboxylate (23). Conversion of the diester into the aldehydo-ester (24) and Wittig reaction then completes a new synthesis of chrysanthemic acid (Scheme 5). 

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