Catalytic, asymmetric synthesis of α-acetoxy amides

Non-racemic cyanohydrin acetates are readily available from aldehydes and potassium cyanide/acetic anhydride by use of bimetallic titanium (salen) catalyst 1. Treatment of the cyanohydrin acetates with a platinum(II) phosphinito catalyst 3 under neutral conditions results in chemoselective hydrolysis to the corresponding α-acetoxy amides in a racemization free process.     

Cyano-Carbonates (I) Efficient Latent Acyl Carbanions

Cyano-carbonates, conveniently prepared in excellent yields by in-situ trapping of cyanohydrin anions with chloroform[acaron]tes under PTC conditions, have been found to be efficient ketone precursors.     

Base Promoted Rearrangement of Carbonate Esters Derived from Aldehyde Cyanohydrins: Application to the Synthesis of α-Keto Esters

Acylation of the cyanohydrin derivative (2) of representative aldehydes with ethyl chloroformate, followed by treatment of the corresponding mixed carbonate esters (3) with lithium hexamethyldisilazide, afforded the cyanohydrin derivative (4) of α-keto esters. Cleavage of the latter (4) with 2,6-lutidine in the presence of silver nitrate led to the procurement of α-keto esters in >50% overall yield.     

Catalytic asymmetric synthesis of O-acetyl cyanohydrins from KCN,Ac2O and aldehydes

A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. This is the first report of the asymmetric synthesis of cyanohydrin derivatives using a cyanide source which is non-volatile and inexpensive.     

One-stage synthesis of adamantyl-containing α-aminonitriles

Reactions of 2-adamantan-2-one, acetone cyanohydrin, and amine lead to the formation of substituted 2-amino-2-cyanoadamantanes. The reaction is of a general character as has been proved by examples on a series of ketones and amines and it proceeds through the formation from the acetone cyanohydrin and amines of 2-amino-2-cyanopropane derivatives reacting further with the carbonyl compounds.     

Reactions of Trimethylsilyl Cyanide with α-Keto Esters: Selective Preparation of Either Methyl 4-(Trimethyl-silyl) oxy-4-cyano-2-oxopentanoate or Methyl 2-(Trimethylsilyl) Oxy-2-cyano-4-oxopentanoate

The reaction of methy1 2,4-dioxopentanoate (3) with TMSCN in the presence of zinc iodide affords the TMS protected cyanohydrin enol ether 4, from which the TMS protected cyanohydrin 1 can be obtained. Treatment of 3 with TMSCN alone gives the isomeric cyanohydrin 2. Reactions of two other α-keto esters with TMSCN are shown to proceed without a catalyst.     

The chemistry of acylals. 3. Cyanohydrin esters from acylals with cyanide reagents

[reaction: see text] When treated with KCN in DMSO at room temperature, acylals from aliphatic aldehydes gave the corresponding cyanohydrin esters in good to excellent yields. Acylals from aromatic aldehydes were less reactive and gave several byproducts in addition to fair yields of cyanohydrin under the same conditions. Trimethylsilyl cyanide mixed with titanium(IV) chloride afforded cyanohydrin esters in good to excellent yields from both aliphatic and aromatic aldehydes.     

Enantioselective cyanosilylation of alpha,alpha-dialkoxy ketones catalyzed by proline-derived in-situ-prepared N-oxide as bifunctional organocatalyst

Bifunctional N,N'-dioxide catalysts have been developed for highly enantioselective cyanosilylation of alpha,alpha-dialkoxy ketones. This process, catalyzed by in-situ-prepared proline-derived N,N'-dioxide 2b, produced the corresponding cyanohydrin trimethylsilyl ethers in excellent yields (up to 99%) with high enantioselectivities (up to 93% ee). A reasonable mechanism was proposed according to the observation of the linear effect, 1H NMR spectra, isolated cyanohydrin, and the roles of the NH and N-oxide moieties of the catalyst.     

Internal oxidation-reduction of quinoxaline-2- carboxaldehyde 1,4-dioxide

Reaction of carboxaldehyde 1 with acetone cyanohydrin gives carboxylic acid 2. Reaction of 1 with acetone cyanohydrin in methanol affords the methyl ester 3. The structural assignment for 2 is supported by ¹³C nmr data and by the decarboxylation of deuterated 2 to give 4b. The internal oxidation-reduction upon going from 1 to 2 is explained in terms of a mechanism whereby 1 is converted into its cyanohydrin 5 and then to acyl cyanide 6. Acyl cyanide 6 then reacts with either water or methanol to give 2 or 3.     

IMPROVED SYNTHESIS OF CYANOHYDRIN PHOSPHATES AND ITS REACTION MECHANISM

Cyanohydrin phosphates 2a–2c were prepared in high yield from ketones (or aldehyde), diethyl phosphorochloridate, and sodium cyanide by using acetonitrile as solvent. GC analysis proved that the two reactions of cyanohydrin sodium with diethyl phosphorochloridate and with diethyl phosphorocyanidate resulted in the formation of cyanohydrin phosphates.     

Crown Ether Catalysis in the Synthesis of Cyanohydrin Derivatives

Carbonyl compounds react with cyanide ion under phase transfer catalysis (18-crown-6) to give cyanohydrin anions which are trapped by acid chlorides, anhydrides or alkylating agents to give cyanohydrin derivatives.     

A facile direct conversion of aldehydes to esters and amides using acetone cyanohydrin

Aromatic aldehydes with electron-withdrawing groups undergo rapid reactions with a variety of alcohols and secondary amines to afford the corresponding esters and amides, respectively, in high yields, when treated with NaCN or acetone cyanohydrin and base under ambient reaction conditions. In case of α,β-unsaturated aldehydes, simultaneous reduction of the CC bond along with esterification occurred to produce the saturated esters in high yields.     

Synthesis of 2-amino-2-cyanoadamantane and its derivatives

Synthetic routes to new amino nitriles with the functional groups at the 2-position of the adamantane core, based on reactions of adamantanonimines with acetone cyanohydrin or of adamantanone cyanohydrin with aliphatic amines, are considered. The products can be used for preparing new biologically active substances, unsymmetrical adamantyl-containing diamines or amino acids.     

Asymmetric synthesis of polymer-supported cyanohydrin acetates

A bimetallic titanium(salen) complex has been used to catalyze the asymmetric addition of potassium cyanide to aldehydes attached to Wang resin giving polymer supported cyanohydrin propionates with up to 91% enantiomeric excesses.     

New approach to the preparation of <Emphasis Type="Italic">p</Emphasis>-(1-cyanoethyl)arenesulfonamides by reaction of arylsulfonyl imines of polychloroacetaldehydes with acetone cyanohydrin

Reaction of N-(2,2,2-trichloroethylidene)- or N-(1-phenyl-2,2-dichloroethylidene)arenesulfonamides with acetone cyanohydrin in acetone in the presence of potassium carbonate led to the formation of N- (2,2,2-trichloro-1-cyanoethyl)- or N-(2-phenyl-2,2-dichloro-1-cyanoethyl)arenesulfonamides.     

Reaction of unsaturated aldehydes with acetone cyanohydrin in the presence of secondary amines

Conclusions Reaction of acetone cyanohydrin with 5-phenyl-2,4-pentadien-1-al in the presence of dimethylamine and with cinnamaldehyde in the presence of piperidine and morpholine is not accompanied by prototropic isomerization and leads to the formation of ,-unsaturated aminonitriles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 953–955, April, 1969.     

Synthesis and properties of Β-(1-uracilyl)-α-hydroxypropionic acid derivatives

-(1-Uracilyl)--substituted propionitriles were obtained by cyanohydrin synthesis from 1-uracilylacetaldehydes. Their hydrolysis, bromination, and amination were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 954–959, July, 1990.     

A novel synthesis of α-fluoroacetonitriles. Application to a convenient preparation of 2-fluoro-2-phenethylamines

α-Fluorophenylacetonitriles (3) are readily prepared by the treatment of the corresponding benzaldehyde cyanohydrin trimethylsilylethers (2) with diethylaminosulfur trifluoride (DAST). This method for the introduction of fluorine alpha to a cyano group is also applicable to the cyanohydrin trimethylsilylethers of aromatic ketones. Diborane reduction of the α-fluorophenylacetonitriles (3) yields 2-fluoro-2-phenethylamines (4).     

Synthetic and mechanistic studies on asymmetric cyanohydrin synthesis using a titanium(salen) bimetallic catalyst

A bimetallic titanium(salen) complex 1 was found to catalyse the asymmetric addition of ethyl cyanoformate to aldehydes. Best results were obtained using 5 mol% of the catalyst at −40 °C and under these conditions, both aromatic and aliphatic aldehydes were converted into cyanohydrin carbonates with up to 99% enantiomeric excess. The same catalyst could also be used to catalyse the asymmetric addition of potassium cyanide to aldehydes in the presence of propionic anhydride, leading to cyanohydrin esters. Mechanistic studies showed that the enantiomeric excess of the product increased during the early stages of this reaction. However, by adding a ‘sacrificial aldehyde’ this effect could be eliminated. The structure of the catalyst in solution was investigated using variable concentration, variable temperature and variable solvent NMR studies. These experiments showed that the catalyst exists as a mixture of monometallic 4 and bimetallic 1 species, a result which is consistent with previous mechanistic studies on the asymmetric addition of trimethylsilyl cyanide to aldehydes and ketones catalysed by the same catalyst. A mechanistic rationale for all of these observations is reported.     

DBU catalyzed cyanoacylation of ketones with acyl cyanides

The reaction of cyclohexanone with benzoyl cyanide catalyzed by amines provides the corresponding O-benzoyl cyanohydrin adducts in moderate to good yields under mild conditions. Among the catalysts, DBU was found to be the most effective promoter allowing the reaction to proceed smoothly at room temperature and to give the corresponding O-acyl cyanohydrin adducts in higher yields for a variety of substituted cyclohexanones, cyclopentanone, acetone or pentan-3-one and various acyl cyanides.