Acyl dianion equivalents

Amide group reduction probably occurs by the mechanism shown in Scheme 3. Two-electron transfer without protonation would give dianion 3. Elimination of LiNMe2 from 3 would give 4 (an acyl anion equivalent) and protonation of 4 at the carbonyl group would give benzaldehyde. 

Allylic 3-(benzotriazoM-yl)-3-ethoxyalkenes are conjugated acyl anion equivalents. Thus, deprotonation with BuLi and reaction with alkyl halides or esters furnish enones and unsaturated a-diketones," respectively. l-(Benzotriazol-l-yl)-3-(diphenylphosphoryl)-l-ethoxy-l-propene is a propanoic ester P, 3-dianion equivalent. 

Acyl anion equivalent. This acid can be converted into the dianion with LDA in THF—HMPT at O. Alkylation followed by oxidative decarboxylation (N-Bromosuccinimide, this volume) with sodium metaperiodate results in an aldehyde, as shown in equation 1. A ketone is obtained by bis-alkylation followed by oxidative decarboxylation (equation II). Note that the carbonyl group is derived from the reagent, which is thus equivalent to the dianion C=0. 

The introduction of a p-oxazilinyl substituent into the aromatic ring of the arylacetal anions (23) stabilizes the anions and allows them to be used as acyl anion equivalents. Bis(ethylthio)acetic acid is a new a-keto-acid synthon. Its dianion reacts with a variety of electrophiles, including aziridines, to give substituted a-keto-acids in fair to excellent yields after deprotection. In two syntheses of /8-keto-acids, R COCl is used as the source of the acyl group. In the first synthesis the dianion of the ethyl ester of malonic acid reacts with R COCl to give... 

Trost has published additional applications of a-lithiocyclopropyl phenyl sulphide, including an approach to spiro-sesquiterpenes, involving geminal alkylation, which utilizes a process that is formally the reversal of dithian-carbonyl addition(also see related studies by Marshall Synthetic applications of the highly nucleophilic methoxy-phenylthio-methyl-lithium PhSCH(Li)OMe and of the acyl anion equivalent methylthioacetic acid dianion RSCHCLOCOgLi (R = Me or Ph ) have also been described, as have synthetic procedures based on anions of a-alkylthio- or a-phenylthio-ketones and methylthiomethyl dithiocarbamates. ... 

Williams and McClymont have observed that acylation reactions of the dianion of 2-(5-oxazolyl)-l,3-dithiane (15) lead to formation of 4,5-disubstituted oxazole products through a Comforth rearrangement pathway under base-induced, low-temperature conditions. For example, deprotonation of 15 with LiHMDS (3.0 equivalents) at -78°C, followed by addition of benzoyl chloride or p-chlorobenzoyl chloride and warming to 0°C, provided 16 in 74% and 47% yield, respectively. 

Single acylation reactions of dianionic cuprates have already been shown in Table 4. After the acylation reactions of these cuprates with one equivalent of an acyl chloride, the resulting lithium enolates can be subjected to a second acylation or alkylation28. The first example shown in Scheme 18 demonstrates such a case, in which the second acylation using benzoyl chloride gave a triketone (Scheme 18). The second example deals with the treatment of the enolate with iodomethane, which resulted in the corresponding 2-methyl-1,4-diketone. 

Another methodology applied to the monosubstitution of diols is the use of copper complexation of dianions. The dianion is first formed by reaction of a diol with two equivalents of NaH. The copper complex is then formed by addition of a copper salt. Reaction of the copper complex with various electrophiles (alkyl halides, acyl chlorides) then gives the selectively protected products. As with the phase-transfer technique, very little disubstitution is observed. However, as illustrated in Scheme 3.16, the regioselectivity is reversed (i.e., 4,6-diols give mainly 4-substitution and 2,3-diols give mainly 3-substitution). Using this technique, both alkylations (benzylation, allylation) and acylations (acetylation, benzoylation, pivaloylation) have been carried out. As usual, the degree of selectivity depends on reaction conditions and structural factors [44]. 

Otherwise a-methoxy allyl sulfides have played the role of an a-methylenated acyl anion (Scheme 76, entry a) or a homoenolate dianion (Scheme 76, entry b) equivalent. 

Dianions of 4- and 6-alkyl-3-cyano-2-pyridones can be formed from the pyridone by treatment with two equivalents of potassium amide in liquid ammonia and can be alkylated, aroylated, or acylated selectively on the... 

Acylation at a is facile (on Q, or -dianions) and requires an extra equivalent of base for the acidic a-acyl sulfone products. Aldehydes and ketones react similarly at a to afford -hydroxy sulfones. Spontaneous cyclization occurred (eq 3) when the al-lylic alcohol from acrolein was oxidized to the unsaturated ketone (eq 3) and treatment with base completed the conversion to 3-methylcyclopentenone. However, mesylation of the -hydroxy sulfone gave the four- instead of six-membered cyclization in eq 3 by direct rather than aUyUc displacement. Other cyclizations are shown in eq 4, the epoxide yielding only the six-membered ring, the dibromo derivative both five- and six-membered rings. 

Besides, when silyl-substituted OCp dianions 31 were subjected into the reactions with acid chlorides, sily 1-shift reactiOTi might occur depending on the reaction condition and the structures of acid chlorides used. When the OCp dianion 31 was treated with one equivalent of electron-deficient, bulky 2,4,6-tilchlorobenzoyl chloride (ArCOCl), the O-acylated intermediate 35 was isolated in 65% isolated yield. Reciystallization of 35 with TMEDA afforded the single-crystals... 

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