Robert L. Lambert

Halomethyl—metal compounds : LXXII. The preparation of α-halocyclopropyl derivatives of lithium and their application in the synthesis of α-halocyclopropyl compounds of silicon, germanium, tin, lead, and mercury. A novel isomerization of syn-7-bromo-anti-7-lithionorcarane to the anti-7-bromo-syn-7-lithio isomer☆

Abstract A number of α-bromocyclopropyllithium reagents have been prepared at low temperature (−90° to −100°) in THF or THF/Et2O medium by reaction of n-butyllithium with the respective gem-dibromocyclopropane. Reactions of these new lithium reagents with concentrated HCl, trimethylchlorosilane, dimethyldichlorosilane, trimethyltin chloride, dimethyltin dichloride, dimethyldichlorogermane, trimethyllead bromide, mercuric chloride and some other organometallic halides are described. A novel isomerization of syn-7-bromo-anti-7-lithionorcarane to anti-7-bromo-syn-7-lithionorcarane, induced by the presence of a slight excess of 7,7-dibromonorcarane, is described.

Halomethyl-metal compounds XX. An improved synthesis of phenyl(trihalomethyl)mercury compounds

Abstract The preparation of PhHgCClnBr3−n (n = 0–2) in good yield can be accomplished by the reaction of phenylmercuric chloride, the respective haloform and the tert-butanol monosolvate of commercial, unsolvated potassium tert-butoxide in ca. 1/1/1.4 molar ratio in tetrahydrofuran solution at -25°. This represents a significant improvement over the previous procedure (ref. 7) in that a high speed stirring apparatus is not required, commercial potassium tert-butoxide may be used and large excesses of the haloform are not necessary.

Halomethyl—metal compounds : LXXIII. Grignard reagents derived from gem-dibromocyclopropanes. α-Bromocyclopropyltin compounds as precursors for α-bromocyclopropyllithium reagents by transmetalation☆

Abstract The reaction of isopropylmagnesium chloride in THF with gem -dibromocyclopropanes gave α-bromocyclopropylmagnesium chloride compounds. When the reaction is carried out at room temperature, these are unstable and carbene-derived products are obtained. At about −70° these reagents are stable and can be used in synthesis. Protolysis gives a mixture of syn and anti isomers when these are possible, but when these Grignard reagents are treated with trimethyltin chloride, only the isomer with the trimethylstannyl substituent in the anti position is obtained. Treatment of syn -7-bromo- anti -7-trimethylstannylnorcarane with n-butyllithium at −95° gave only syn -7-bromo- anti -7-lithionorcarane; stereospecific reactions of this reagent with CO 2 and hexachloroethane are described. In situ Grignard-Wurtz reactions were used to prepare 7,7-bis(trimethylsilyl)- and 7,7-bis(trimethylstannyl)norcarane.

Halomethylmetal compounds : LI. An improved synthesis of α-iodoalkyl derivatives of tin and mercury by the organozinc route. Bis[(trimethylsilyl)iodomethyl]mercury☆

Abstract The homogeneous solution of iodomethylzinc iodide produced by reaction of equimolar quantities of ethylzinc iodide and diiodomethane in tetrahydrofuran was used to prepare Me 3 SnCH 2 I, Me 2 Sn(CH 2 I) 2 and Hg(CH 2 I) 2 in good yield; this procedure is much superior to that using the reagent prepared from the reaction of diiodomethane with zinc/copper couple. The reaction of ethylzinc iodide with CH 3 CHI 2 , Me 3 SiCHI 2 and Me 3 SnCHI 2 in THF gave good yields of CH 3 CHIZnI, Me 3 SiCHIZnI and Me 3 SnCHIZnI, respectively. These reagents were used to prepare, generally in high yield, the following compounds: Me 3 SnCHICH 3 , Hg(CHICH 3 ) 2 , Me 3 SiCHISnMe 3 , Hg(CHISiMe 3 ) 2 and (Me 3 Sn) 2 CHI. The Hg(CHISiMe 3 ) 2 /Ph 2 Hg reagent pair was found to transfer Me 3 SiCH to cyclohexene and cyclooctene, but the silylcyclopropane product yields were quite low.

Halomethyl-metal compounds

Abstract The phenyl(dihalocarboalkoxymethyl)mercury compounds PhHgCCl 2 CO 2 CH 3 , PhHgCClBrCO 2 CH 3 , PhHgCBr 2 CO 2 CH 3 , PhHgCCl 2 CO 2 CH 2 CHCH 2 and PhHgCCl 2 CO 2 CMe 3 have been prepared by the reaction of phenylmercuric chloride, the appropriate dihaloacetic acid ester and Me 3 COK · Me 3 COH in THF at −50° to −65°. The first two mercurials were found to transfer ClCCO 2 CH 3 to olefins and to triethylsilane, while the third proved to be a source of BrCCO 2 CH 3 . The rather high stability of these mercury compounds, however, limits their application in the synthesis of carbomethoxy-substituted cyclopropanes.

Halomethyl—metal compounds : LXXIV. Organolead compounds as precursors for halo- carbenes

Abstract The following organolead compounds were prepared and investigated as potential divalent carbon transfer agents: Ph3PbCCl3, Ph3PbCBr3, Ph3PbCCl2Ph, Ph3PbCHCl2 and Ph3PbCHClF. Of these the CCl3, CBr3 and CHCl2 compounds were found to be useful carbene sources at higher (120–150°) temperature. The reaction of triphenylleadlithium with 3,3,3-trichloropropene gave hexaphenyldilead and Ph3PbCH2CHCC2, rather than the expected Ph3PbCCl2CHCH2.