Acyl-lithiums and their Equivalents

Seebach, B. Scoring, H.-O. Kalinowski, W. Lubosch, and B. Renger, Angew. Chem. Internet. Edn., 1977,16, 264. 

Thioacetal anions and related anions of type (3 X, Y = SMe or SiMea) can be obtained by addition of organolithiums (RLi) to the corresponding compounds (4). On the other hand, compounds of type (4 X = Br, SePh, or SnBua) react with Bu Li to give o-heteroatom-substituted vinyl-lithiums (5), which in cases where Y = SPh or SePh are themselves acyl carbanion equivalents. Interestingly, the vinyl-lithium (5 Y = SPh) can also be used as a source of compounds (4 Y = SPh, 

X = SePh, SR, SiMca, or SnBu 3) by its reactions with PhSeBr, RSSR, MeaSiCl, or Bu 3SnCl. Lithiation of the cw-enedithiol ether (6) with Bu Li or LiNPr 2 gives the further modified acyl carbanion equivalent (7) which reacts with electrophiles ( ) to give compounds of type (8).  

Cyclic vinyl ethers such as (9) are lithiated to give acyl carbanion equivalents (10), whilst a-substituted vinyl-lithiums of type (11) react with aldehydes and ketones, ArCOR, to give substituted 2-butenolides (12).  

LiC(0Me)2C02Me is a carbomethoxycarbonyl anion equivalent,whilst species (13) provides yet another approach to simple nucleophilic acylation. In the latter case intermediate trimethylsilyloxirans, e.g. (14) (from reaction with cyclohexanone), are converted into the carbonyl compounds by treatment with acid, but alternatively they may be converted into other compounds by appropriate choice of reagents.  

Acyl-lithiums and their Equivalents. Acyl-lithiums are amongst the most sought-after synthons, but to date they have been synthesized directly only for amide types (1). Thus, (1 = Pr ) has been obtained by the reaction of AW-bis(2-propyl) 

Protected cyanohydrin anions also behave as acyl carbanion equivalents, and this method can be extended to aj3-unsaturated derivatives (5). The reaction of yet another type of acyl carbanion equivalent (6) with esters gives products of type (7), which are useful for the synthesis of novel heterocyclic compounds. Species of type (8 Y = 0,S), are further modified acyl carbanion equivalents, and behave towards carbonyl compounds as synthetic equivalents of the Wittig reagents PhaP = C(YR)CHO. Compounds (9) are j8-acylvinyl anion equivalents.  

The species (10) and (11), may be considered as synthons for HSCH2 and H0(CH2) CH2 respectively, whilst (12) reacts with aldehydes and ketones to give oxiranes. Selenium is capable of stabilizing an adjacent carbanion centre in the same way as sulphur, and reaction of diselenoketals with Bu Li provides a convenient approach to reagents of type (13). After alkylation, hydroxyalkylation, or acylation of (13) the selenium can be removed reductively, by oxidative elimination, or, in the case of 2-hydroxy compounds, by elimination to form an oxirane, so the synthetic potential is clear. 

Furukawa, and G. Tsuchihashi, Synthesis, 1976, 202 M. Julia, D. Uguen, and A. Callipolitis, Bull. Soc. chim. France, 1976, 519. 

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Acyl-lithiums and their Equivalents. Details have appeared of the preparation of di-isopropylcarbamoyl-lithium (LiCONPr a) by reaction of di-isopropylformamide with t-butyl-lithium. Lithiated dithioacetals, particularly those derived from dithians, continue to be popular. Alkylations of such species have been important reactions in syntheses of 25-hydroxycholesterol, pyrenophorin and vermiculin," and several chain-elongated sugars. 2-(3,3-Dialkoxypropyl)-l,3-dithians may be converted via their lithiated derivatives into protected 2-hydroxycycIobutanone derivatives (Scheme 1), themselves potential synthons for 1,4-diketones and cyclopentenones. ... 

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