Metalation reactions—VIII Metalation of 1,4-enynes and protonation of their anions

A series of 1,4-enynes was prepared and the compounds metalated with butyllithium in ether. The formation of the mono- and dilithio derivatives was studied by PMR and UV. Protonation of the dilithio compounds gave vinylallenes, 1,3- and 1,4-enynes. Isomerisation of the 1,4-enynes in DMSO using dimsylsodium gave vinylacetylenes from compounds containing a terminal double bond and vinylallenes from those with an internal double bond. The sequence of the H—D exchange of the various protons was also studied.     

Metalation of bromodiazines. Diazines XL

The syntheses of 2‐bromopyrazine, 2,4‐dibromopyrimidines, and 3‐bromo‐6‐phenylpyrazine were improved and their metalation with lithium alkylamides was studied.     

Metalation of methoxy- and 1,1′-dimethoxyferrocenes

Conclusions 1-Methoxyferrocene-2-carboxylic acid, 1,1-dimethoxyferrocene-2-carboxylic acid, and 2-methoxy-ferrocenyl diphenyl carbinol have been obtained via the lithium derivatives of methoxy- and 1,1-dimeth-oxyferrocenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1867–1869, August, 1967.The authors express their thanks to V. N. Drozd for much valuable advice in the performance of this work.     

Metalation reactions. : IV. Metalation of o-alkyl- and o,o′-dialkyl-substituted alkylthiobenzenes

Metalation of o-alkyl- and o,o′-dialkylsubstituted alkylthiobenzenes with n-butyllithium, in the presence and absence of TMEDA, has been investigated. The results showed that metalation at the thioalkyl carbon probably occurs by direct attack of the organolithium reagent, although a transmetalation reaction cannot be excluded in some cases. It has also been found that benzylic, thio-methylic, and ring metalation occurs in ether alone, whereas mainly thio-methylic or ring metalation occurs in the presence of TMEDA.     

Metalation of t-butyl sulfoxides,sulfones and sulfonamides of pyridazine and pyrazine. Metalation of diazines. XX

In the pyridazine series, the use of tert-butylsulfinyl and tert-butylsulfonyl as ortho directing groups for metalation has been tested. Various functionalized products were obtained in good yields. In the case of 3-tert-butylsulfinyl-6-methoxypyridazine, the metalation was regioselective in ortho to the sulfinyl group. The metalation of 2-tert-butylsulfinyl and 2-tert-butylsulfonylpyrazine gave low to moderate yields. Synthesis of diazinesulfonamides were improved and the metalation of N-tert-butylsulfonamidopyrazine was achieved.     

Metalation of diazines. VI. Metalation of pivaloylaminopyrazine and N-t-butylpyrazinamide. Unusual regioselectivity in the metalation reaction

Metalation of pivalamidopyrazine and N-t-butylpyrazinamide were studied. For pivalamido pyrazine the yields were poor and some addition products were isolated. The metalation of t-butylpyrazinamide was successful and a curious regioselectivity was highlighted.     

A synthetic strategy leading to monodisperse PPV oligomers by coupling reactions of vinyltrimethylsilanes

A novel strategy for the synthesis of well-defined oligo(phenylenevinylene)s was developed. The procedure is entirely based upon two coupling processes, both involving vinyltrimethylsilanes. Bis(styryl)benzenes 2a-g bearing two octyloxy groups in the central aromatic ring and various substituents on the external aromatic rings were prepared in good yield by a regio- and stereoselective coupling reaction of 1 with different arenediazonium tetrafluoroborates. Oligomers with a more extended conjugated system, 4a-c, and with m-phenylene subunits 13a,b, were also readily obtained by conversion of the unsaturated trimethylsilyl derivatives 3a,c,d to the corresponding boron derivatives and a subsequent coupling reaction with compounds 2a and 2c.     

Ring Formylation of Bromobenzoate Esters by Direct Metalation

A study on the synthesis of a benzaldehyde containing an ester function directly from tert-butyl 4-lithiobenzate was described. t-Butyl 4-bromobenzoate reacted with butyllithium at -78°C in THF, followed by immediate addition of DMF to give the desired benzaldehyde in moderate yield. The scope of this reaction was examined.     

Asymmetric Induction through Metalation of Chiral Dithioacetals and Oxathioacetals

Abstract

The work presented in this article consists of synthesis of chiral dithioacetals and oxathioacetals using pure chiral auxiliaries, such as, (+) camphor, (?) menthol, and L‐cysteine. Metalation of these chiral dithioacetals and oxathioacetals, followed by nucleophilic addition to benzaldehyde and removal of chiral auxiliary, furnished scalemic mandelic acid with various enantiomeric purities.     

Synthesis of ortho-substituted aminopyridines. Metalation of pivaloylamino derivatives

The three isomeric pivaloylaminopyridines were lithiated in more than 80% yields. Aminopyridine derivatives were treated by 2.5-3 equivalents of the complex BuLi-TMEDA at −10° in diethyl ether. Reaction of the lithiated species with various electrophiles afforded a number of ortho-substituted pivaloylaminopyridines in good yields. Secondary pyridine alcohols were oxidized to the corresponding aminopyridyl ketones. Pyridopyrimidines, benzonaphthyridines as well as an analogue of the natural antitumor alkaloid ellipticine has been synthesized showing the versatility of the method.     

Metalation of toluene and cumene with alkali metal-crown ether complexes

Metalation of toluene and isopropylbenzene with alkali metal-crown ether complexes led to the corresponding α-metalated alkylbenzenes. Treatment of the latter in succession with solid carbon dioxide, water, and hydrochloric acid gave carboxylic or dicarboxylic acids in 65–78% yield. Metalation of isopropylbenzene with sodium or potassium crown ether complexes above 90°C was accompanied by cleavage of the polyether ring with formation of organometallic compounds which then reacted with isopropylbenzene to produce 2-sodio(potassio)-2-phenylpropane and open-chain oligoether.     

Directed ortho Metalation reaction of aryl O-carbamates on solid support

The first Directed ortho Metalation (DoM) reaction of aryl O-carbamates on polystyrene-divinylbenzene (PS-DVB) resin using a trityl linker is described. Using low temperatures and short metalation times, a range of electrophiles have been introduced to give, after cleavage from support, substituted benzyl alcohols in high purity. [reaction: see text]