Carbonyl anions, addition

In 2006, Scheidt and coworkers [44] reported the first enantioselective direct nucleophilic addition ofthe silylated thiazolium salt 148, a precursor of the equivalent acyl anion, to nitroalkene 149 in the presence of tetramethylammonium fluoride (TMAF) and stoichiometric amounts of quinine-based thiourea 81b, producing the chiral [3-nitroketone 150 in 67% yield and with 74% ee (Scheme 9.51). The acyl anion equivalent 152 can be generated by the desilylation of 148 with TMAF, followed by the 1,2-H shift of the resulting alkoxide 151. The observed asymmetric induction indicates that there is a strong interaction between the thiourea and the nitroalkene during the carbonyl anion addition step. 

Aldol Addition and Related Reactions. Procedures that involve the formation and subsequent reaction of anions derived from active methylene compounds constitute a very important and synthetically useful class of organic reactions. Perhaps the most common are those reactions in which the anion, usually called an enolate, is formed by removal of a proton from the carbon atom alpha to the carbonyl group. Addition of this enolate to another carbonyl of an aldehyde or ketone, followed by protonation, constitutes aldol addition, for example... 

Carbonyl hydrides and carbonylate anions are obtained by reducing neutral carbonyls, as mentioned above, and in addition to mononuclear metal anions, anionic species of very high nuclearity have been obtained, often by thermolysis. These are especially numerous for Rh and in certain Rh, Rh and Rhi5 anions have structures conveniently visualized either as polyhedra encapsulating further metal atoms, or alternatively as arrays of metal atoms forming portions of hexagonal close packed or body... 

Anionic phosphorus has been used as well in a number of recent reports of additions to carbonyl compounds. Addition of dialkyl phosphite to aromatic aldehydes in the presence of catalytic amounts of La-BINOL and dilithium (R)-binaphthoxide occurs enantioselec-... 

Thallium(i) salts have long been used in reactions with organic and organometallic halide complexes as a means of activating the halide by removal as insoluble T1X. However, the thallium ions proved not to be innocent bystanders, and numerous examples were reported in COMC (1995) where the metal-bound thallium complexes were formed. Deliberate reactions of thallium(i) and thallium(m) salts with metal carbonyl anions have yielded a variety of complexes of the form T1 MLJ3. In the past decade, new examples of metal carbonyl derivatives of thallium have been prepared (see Table 2). In addition, the propensity for Tl+ to form adducts with 16-electron noble metal complexes has been exploited. 

Complexes M(CH2C CC=CMe)(CO)nCp [325 M = Mo, n = 3 M = Fe, = 2 (Scheme 74)] were obtained from the carbonyl anions and l-chlorohexa-2,4-diyne. Subsequent chemistry involves protonation (HBF4) to cationic allene or diene complexes, or addition of MeOH to give allylic derivatives, which are formed with concomitant insertion of CO. The latter can also be obtained from the cationic species and NaOMe. The allene-iron cation reacts with NHEt2 to form an ynenyl complex. The luminescent complex Re(CO)3(5,5 -Bu 2-bpy) 2 (At-C=CC6H4C CC=CC6H4C=C) has been reported. ... 

Scheldt and co-workers have reported the apphcation of silyl-protected thiazoUum carbinols as stoichiometric carbonyl anions for the intermolecnlar acylation of nilroalkenes [89]. While predominantly a discussion of racemic chemistry, a singular example illustrates that the newly formed stereocenter may be controlled by the addition of an equivalent of a chiral thionrea 136 with the desired product 135 formed in 74% ee Eq. 13. 

The addition of Mo(CO)3 fragments to iron carbonyl anions has also been used to synthesize iron-molybdenum-sulfur compounds. Thus, the reaction between... 

Oxathiolane 3,3-dioxide (332) metallates in its 2-position to yield an anion which reacts with various electrophiles (alkyl halides and carbonyl compounds) to give substituted oxathiolanes (333) in good to excellent yield (79TL3375). Pyrolysis of these alkylated products affords the corresponding aldehydes or 2-hydroxyaldehydes in addition to sulfur dioxide and isobutylene (Scheme 71). The oxathiolane (332) thus becomes another member of the already burgeoning class of carbonyl anion equivalents. 

IR data established a clear distinction between the predominant rhodium species in the absence and in the presence of amine, i.e., in reaction systems producing aldehyde and alcohol, respectively. Rhodium carbonyl anions, normally absent, are formed on addition of amine. No significance is attached to the differences between monomer and polymer behavior since a facile interconversion among the various carbonyl anions is well established (18). 

IR data supported the formation of rhodium carbonyl anions on addition of amine suggesting a mechanism in which these anions are in equilibrium with the active species, a hydrido rhodium carbonyl containing coordinated amine. Such a mechanism provides an explanation for the variation in catalyst activity with amine concentration and basicity and affords a method for predicting the effect of other amine ligands. 

Several useful variations of the tetracarbonyliron dianion-alkyl halide reactions are known. These employ the iron complex stoichiometrically, however. Since the dianion is much more nucleophilic than the alkyliron monoanion, the reaction can easily be stopped at the monoalkylated stage. Carbonylation or addition of another good ligand such as triphenylphos-phine to the monoalkylated complexes produces monoacyliron anions. Pro-... 

The most extensive series of compounds that fall within this section are the anionic iron carbonyl-thallium clusters recently described by Whitmire (30-30h). These are generally made by reactions between iron carbonylate anions and either T1(I) or Tl(III) salts. Thus treatment of K[HFe(CO)4] with a variety of thallium salts followed by addition of [Et4N]Cl or Br affords the hexanuclear complex [Et4N]2[ Fe(CO)4 2 //-TlFe(CO)4 2], 17... 

This process has been coupled with meta addition of a carbonyl anion equivalent and the controlled exo addition of the incoming nucleophile to generate acorenone and acorenone B stereospecifically from [(o-methylanisole)Cr(CO)3] (63 Scheme 14).123 The first step is addition of a cyanohydrin acetal anion (64) to the less-hindered meta position in [(o-methylanisole)Cr(CO)3]. Addition of allylMgBr to the resulting ketone, anti-Markovnikov addition of HBr to the alkene, substitution for Br by CN, and coordina-... 

Organolithiums have been shown to add to a variety of trithiocarbonate oxides exclusively in a thiophilic maimer, as a consequence of the electrophilic character of the sulfine sulfur, to give an intermediate carbanion stabilized by three sulfur atoms the soft carbanion, which forms trithioorthoester oxide on quenching with water, acts as the equivalent of the (alkylthio)carbonyl anion in Michael addition.98... 

Conjugate addition of acyl groups to naphthoquinones (3, 211).2 The acyl nickel carbonylate anion (1) undergoes conjugate addition to the ethylene ketal 2 to form a lithium adduct that can be trapped by allyl iodide to give 3 in 81% yield. This product can be converted in a few steps to the hydroxyquinone 4, a precursor of the naphthoquinone antibiotic deoxyfrenolicin (5). 

Another example concerning the reduction of carbonyl compounds also relates to the salt effect theme. Shaefer and Peters (1980), Simon Peters (1981,1982,1983,1984), Rudzki et al. (1985), and Goodman and Peters (1986) described photoreductions of aromatic ketones by amines. In this case, the addition of excess NaC104 results in considerable retardation, even prevention, of final product formation. The two fundamental steps in this photoreduction consist of rapid electron transfer from the amine to the photoactivated ketone (in its triplet state), followed by the slow transfer of proton from the amine cation radical to the carbonyl anion radical ... 

An unusual synthesis of acyldienes from conjugated dienes, carbon monoxide, and alkyl or acyl halides using cobalt carbonylate anion as a catalyst should be mentioned here (57). The reaction apparently involves the addition of an acylcobalt carbonyl to a conjugated diene to produce a l-acylmethyl-7r-allylcobalt tricarbonyl, followed by elimination of cobalt hydrocarbonyl in the presence of base. The reaction can thus be made catalytic. Since the reaction was discussed in detail in the recent review by Heck (59), it will not be pursued further here. 

The conjugate addition of carbonyl anions catalysed by thiazolium salts (via umpol-ung) that is fully operative under neutral aqueous conditions has been accomplished. The combination of a-keto carboxylates (157) and thiazolium-derived zwitterions (e.g. 160) in a buffered protic environment (pH 7.2) generates reactive carbonyl anions that readily undergo conjugate additions to substituted o /3-unsaturated 2-acylimidazoles (158) to produce (159). The scope of the reaction has been examined and found to accommodate various a-keto carboxylates and /3-aryl-substituted unsaturated 2-acylimidazoles. The optimum precatalyst for this process is the commercially available thiazolium salt (160), a simple analogue of thiamine diphosphate. In this process, no benzoin products from carbonyl anion dimerization were observed. The resulting 1,4-dicarbonyl compounds (159) can be efficiently converted into esters and amides by way of activation of the A-methylimidazole ring via alkylation.181... 

Nitro compounds can be alkylated and are good at conjugate addition (chapter 21) so the products of these reactions can be used to make aldehydes, ketones and amines. A simple synthesis of octanal5 shows that these methods can work very well indeed. Alkylation of nitromethane with bromoheptane gives the nitro-compound 11. Formation of the anion 12 and oxidation with KMnC>4 gives octanal in 89% yield. This chemistry gives us the disconnection to an alkyl halide and a carbonyl anion. The anion 12 is an acyl anion equivalent and we shall need these in the next chapter. 

Trithiocarbonate S-oxides are reactive towards alkyllithiums [111] thio-philic additions were carried out at -78 °C. The resulting carbanions, stabilised by three sulfur groups, were quenched by water or by other electrophiles to afford trithioorthoester oxides. With enones, 1,4-addition was observed elimination of an alkanesulfenic acid led to /1-oxoketenedithioace-tals which could be transformed into 4-oxoalkanethioates. This Umpolung route allows the formal use of an (alkylthio)carbonyl anion. 

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