Acyl carbanion

Reactions with Acyl Garbanion Equivalents. Alkyl substituted carbanions CRXY with potential leaving groups X, Y, and acyl carbanion equivalents or CHRX (342) react with alkylboranes, providing products with mixed alkyl groups derived from both reagents. 

Bis(dimethylamino)carboniiim bifluoride catalyzes the addition of acyl fluorides to perfluoroalkenes by the generation of readily acylated carbanions [4] (equation 4)... 

Dithioacetals are useful in organic synthesis as protective groups for carbonyl compounds, as precursors of acyl carbanion equivalents or as electrophiles under Lewis acidic conditions. The DBSA-catalysed system was also found to be applicable to dithioacetal-ization in water. In addition, easy work-up has been realized without the use of organic solvents when the products are solid and insoluble in water. In fact, the dithioacetaliza-tion of cinnamaldehyde on 10 mmol-scale with 1 mol% of DBSA proceeded smoothly to deposit crystals. The pure product was obtained in excellent yield after the crystals were filtered and washed with water (Equation (8)). This simple procedure is one of the advantages of the present reaction system. 

Stork, c ., Ozorio, A. A., and Leong, A. Y. W., N,N-Diethylaminoacetonitrile, a generally useful latent acyl carbanion. Tetrahedron Lett, 5175, 1978. 

The deprotonation and addition of a base to thiazolium salts are combined to produce an acyl carbanion equivalent (an active aldehyde) [363, 364], which is known to play an essential role in catalysis of the thiamine diphosphate (ThDP) coenzyme [365, 366]. The active aldehyde in ThDP dependent enzymes has the ability to mediate an efScient electron transfer to various physiological electron acceptors, such as lipoamide in pyruvate dehydrogenase multienzyme complex [367], flavin adenine dinucleotide (FAD) in pyruvate oxidase [368] and Fc4S4 cluster in pyruvate ferredoxin oxidoreductase [369]. 

In dithioacetals the proton geminal to the sulfur atoms can be abstracted at low temperature with bases such as Bu"Li. Lithium ion complexing bases such as DABCO, HMPA and TMEDA enhance the process. The resulting anion is a masked acyl carbanion, which enables an assortment of synthetic sequences to be realized via reaction with electrophiles. Thus, a dithioacetal derived from an aldehyde can be further functionalized at the aldehyde carbon with an alkyl halide, followed by thioacetal cleavage to produce a ketone. Dithiane carbanions allow the assemblage of polyfunctional systems in ways complementary to traditional synthetic routes. For instance, the p-hydtoxy ketone systems, conventionally obtained by an aldol process, can now be constructed from different sets of carbon groups. ... 

The most systematically investigated acyl anion equivalents have been the IMS ethers of aromatic and heteroaromatic aldehyde cyanohydrins, TBDMS-protected cyanohydrins, benzoyl-protected cyanohydrins, alkoxycarbonyl-protected cyanohydrins, THP-protected cyanohydrins, ethoxyethyl-protected cyanohydrins, a-(dialkylamino)nitriles, cyanophosphates, diethyl l-(trimethylsiloxy)-phenylmethyl phosphonate and dithioacetals. Deprotonation of these masked acyl anions under the action of strong base, usually LDA, followed by treatment with a wide variety of electrophiles is of great synthetic value. If the electrophile is another aldehyde, a-hydroxy ketones or benzoins are formed. More recently, the acyl carbanion equivalents formed by electroreduction of oxazolium salts were found to be useful for the formation of ketones, aldehydes or a-hydroxy ketones (Scheme 4). a-Methoxyvinyl-lithium also can act as an acyl anion equivalent and can be used for the formation of a-hydroxy ketones, a-diketones, ketones, y-diketones and silyl ketones. - ... 

Enders, D., Breuer, K. Addition of acyl carbanion equivalents to carbonyl groups and enones. Comprehensive Asymmetric Catalysis l-lll 1999,3, 1093-1102. 

Cyclopentanone annulation via a cyclopropoxide anion has great synthetic applicability. Construction of the D-ring in estrone can be achieved by base-induced intramolecular cyclization of an appropriately substituted cyclopropanol using sodium hydride as base (Table 2, entry 23-24 jjjg j-esyit is well accounted for by assuming intramolecular carbonyl addition of a j3-acyl carbanion. 

Thiamin is involved in the stabilization of the acyl carbanion intermediate and is particularly important in carbohydrate metabolism [87]. 

Addition of Acyl Carbanion Equivalents to Carbonyl Groups and Enones... 

The product, a-acetolactate, is formally derived from the acyl carbanion generated by the decarboxylation of pyruvate with a second molecule of pyruvate. The formation of lactylthiamin diphosphate on the enzyme generates initially the unprotonated adduct, which contains the enamine equivalent of a carbanion. This can add to the carbonyl group of a second molecule of pyruvate to form acetolactate (Scheme 35). 

However, with nitro-substituted carbanions, attack occurs at C-2 to give the stable adducts (69) (Scheme 7), the structures of which have been assigned on the basis of their mass spectral fragmentation patterns. With acyl carbanions the oxadiazinium salts undergo an ANRC)RC process... 

Chamberlain, W.J. Polar lipid materials in cigarette smoke condensate Tob. Sci. 20 (1976) 168-170. Chedekel, M.R. 1. Aberrant biosynthetic studies in Nicotiana tabacum and Nicotiana glauca. 11. Synthetic studies of the tobacco alkaloids. 1,4-Additions to acyl carbanion equivalents Dissertation Abstr. (1973) 2519. Chen, C.M. and D.K. Meltiz Cytokinin biosynthesis in a cell-free system from cytokinin-autotrophic tobacco tissue cultures FEBS Lett. 107 (1979) 15-20. 

A full report has appeared on the direct lithiation of NN-di-isopropylformamide by t-butyl-lithium and the use of the acyl carbanion thus obtained in the synthesis of a-keto-amides. The lithium enolate of NN-dimethylacetamide has been isolated for the first time, as a white solid, and has been shown to react well with a usual range of electrophiles. A Canadian group have also discussed the synthesis and reactions of such enolates, in particular their behaviour with ketones from which 70% yields of jS-hydroxyamides can routinely be obtained. " These enolates when generated as in the above methods, using lithium di-isopropylamide, also afford good yields of a-(methylthio)-amides when treated with dimethyl disulphide, in contrast to when sodium in liquid ammonia is used as base, which results in polysulphenylation of the amide. ... 

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). ... 

An interesting development in the lithiated cyanohydrin ether approach to acyl carbanion equivalents involves the [2,3] sigmatropic rearrangement of the anions derived from allyl- or propargyl-cyanohydrin ethers/ Scheme 2 shows an example of the application of this process in the synthesis of y-dicarbonyl compounds or their monoenol ethers. ... 

---