Intramolecular Trapping of Esters by 1-Lithio-1-bromocyclopropanes

Syntheses ofgem-Dihalocyclopropanes and Their Use in Organic Synthesis

“…The reaction of 1,1-dibromo-2-phenylcyclopropane with dilithium tetramethyl zincate followed by oxidation of the resulting cyclopropyl zincate by VO-(OEt) 2 Cl 2 leads to substitution of one or both of the bromides by a methyl group. 366 The reactions of gem-dibromocyclopropanes possessing an ester functionality with methyllithium at -90 °C proceed as an intramolecular trapping of lithium bromocyclopropane by an ester carbonyl group to form five-membered rings with high stereoselectivity 210,367 (eq 80). 367 These five-membered ring products could be the result of a stereoselective metal-halogen exchange, leading to the syn-lithium ester, or of the formation and equilibration of two isomeric lithiobromides, where only one isomer cyclizes.…”

“…This keto alcohol then undergoes Michael cyclization with the formation of a bicyclic ketone (eq 81). 210,367 The reactions of 2-acylaminomethyl-1,1-dibromocyclopropanes with methyllithium proceed similarly (eq 82). 210,368 Knochel recently described the stereoselective formation of the cis-magnesium carbenoid from 1,1dibromo-2-ethoxycarbonyl-2-methylcyclopropane and isopropylmagnesium bromide in diethyl ether at -50 °C.…”

Synthesis of 1-Bromosubstituted Analogs of cis-Deltamethrinic and cis-Permethrinic Acids

“…In analogous reactions 1-acylaminomethyl-2,2-dibromocyclopropane (XII) rearranged nearly quantitatively into the corresponding bromoaminomethyl ketone XIII even in the case of N-trifluoroacetyl derivative XII [17] (Scheme 7), whereas the trifluoroacetate of 2,2-dibromocyclopropylmethanol did not yield products of trifluoroacetyl group transfer [14].…”

“…The reaction of esters of 2,2-dibromocyclopropylmethanols with methyllithium is known to result in a cis-1,4-O,C-migration of the acyl group initiated by the replacement of the cis-bromine by lithium (Scheme 2, transitions II > III > IV) [14].…”

“…The low stereoselectivity of hydrodebromination of compound VIIc also should be noted (the ratio of cis-and trans-isomers of compound X was 1:1.36] that apparently suggests the lack of coordination of the organolithium compound to the dichloroacetyl group prior to the attack on the carbonbromine bond of the small ring (cf. [14,17]). …”