Potassium tert-butox

Ketene acetals react with dichloro(phenyl)methane and sodium134 or potassium tert-butox-ide134,135 to afford t,l-dialkoxy-2-chloro-2-phenylcyclopropanes, e.g. 5,134 which generally enter readily into further reactions. 

A reaction of haloforms with a base, which generates dihalocarbenes (a-elimination) and their addition to alkenes is an efficient method for the preparation of 1,1-dihalocyclopropanes, with the exception of 1,1-difluoro derivatives (Houben-Weyl, Vol.E19b, pp 1464-1466). When chlorodifluoromethane and an alkene are treated with methyllithium,3,4 potassium tert-butox-ide,5,6 powdered sodium hydroxide in tetraglyme7 or a concentrated aqueous solution of alkali metal hydroxide and a phase-transfer catalyst,8-9 the expected 1,1-difluorocyclopropanes are formed in low yields. Comparable low yields of these products result, if dichlorodi-fluoromethane and an alkene are treated with methyllithium.3,4 The main products formed are those that result from reaction of difluorocarbene (carbenoid), and its precursor, with the base or the solvent present in the system (for examples, see refs 10-12). Therefore, the reaction of chlorodifluoromethane with base and an alkene lacks preparative value, The difficulties mentioned above are circumvented in the method using chlorodifluoromethane, oxirane (or chloromethyloxirane), with tetraalkylammonium halide as a catalyst and an alkene6 (Houben-eyl, Vol. 4/3, p 380 and Vol. E19b, pp 1468-1469). 

Also 2,2,2-triphenylethyllithium reacts with excess potassium tert-butox-ide in THF at -TST to give complete rearrangement of carbon skeleton in less than 10 minutes (45) this reaction is believed to occur by way of intermediate 2,2,2-triphenylethylpotassium (44). 

Silyl ethers incorporating an a-haloallg lsilyl moiety have been used to generate a-silyl radicals for radical cyclization (Scheme 17). Recent progress in the radical cydization of (aUyloxy)(bromomethyl)silanes, pioneered by Stork ] and Nishiyama, is summarized in an excellent review. The initial product 53 of the reaction of silyl ether 52 is oxidatively cleaved to give a diol 54. Alternatively, treatment of 53 with potassium tert-butox-ide in dimethyl sulfoxide gives the methyl-substituted alcohol 55. Exceptional levels of stereocontrol are obtained in the acyclic series (e.g., 56 57). xhe reaction is usually... 

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