Aldol condensation acetonitrile

In the nitrogen analogue of the aldol condensation, nitrosoarenes condense with arylacetonitriles to produce cyanoimines [39]. When two equivalents of the acetonitrile is used, further condensation occurs to form [J-cyanovinylamines (Scheme 5.29) [40],... 

In contrast with the reactions of the imino esters, the aldol condensation of imino nitriles and aromatic aldehydes in dichloromethane produces azabutadienes (Scheme 6.17), with the Z-isomers predominating often to the exclusion of the E-isomers [43, 44], Yields generally tend to be at least 10% lower when the reaction is conducted in acetonitrile. 

It was suggested73 that the most probable mechanism of this reaction is an initial aldol condensation of the starting ketone leading to the a,/ -unsaturated ketone 100 or to the /Miydroxyketone 101 which serve as precursors to the tertiary carbenium ions 102, which reacts in turn with nitriles by an acid-catalyzed Ritter reaction to give 103 (equation 36). This suggestion is confirmed by the results of a cross-reaction experiment of benzaldehyde and diethyl malonate with acetonitrile to give 14 (equation 37). 

Pro-azaphosphatranes lb. Id, and 9b catalyze the reaction of aldehydes with acetonitrile to give the title compounds in very good to excellent yields [124]. In a comparison of the efficacy of le with Id in several cases, le was more effective but If was quite inactive [71]. Aldehydes taking part in this reaction form secondary alcohols which are less sterically hindered and can be more easily depro-tonated, thus leading to a,jS-unsaturated nitriles. Primary aldehydes, however, undergo aldol condensation. 

Thus allyl alcohol, methallyl alcohol and crotyl alcohol give only about 2 % of the y-lactones under the reaction conditions usually applied in the ring closure reaction. However, the selectivity towards lactones is increased with the use of acetonitrile or its derivatives as solvents and with addition of small amounts of organic bases such as pyridines in combination with acetonitrile. A 60 % yield of y-butyrolactone may be obtained under these conditions [835], while the rest of the starting materials isomerize to the corresponding aldehydes. These undergo further reactions such as the aldol condensation, or polymerize at higher temperatures. 

Many examples of useful synthetic procedures based on amino- or oxy-boranes have been reported. Substituted anilines undergo ortAo-acylation by RC=N in the presence of BCI3, via the aminodichloroborane. Indoles and l-acyl-3-indolinones are obtained by further modification. " N-Alkylanilines are ortho-formylated by isocyanides (and hydrolysed) under similar conditions. The major reaction of such species, however, is aldol-type condensation. Acetonitrile or PhCH2CN condenses with ArCHO in the presence of R2NBCI2, for instance,... 

Likewise a-keto and a-aldehydo esters have been prepared by the reaction of potassium phenylacetate with a-bromo ketones or aldehydes by an 18-crown-6 catalyzed displacement reaction in acetonitrile or benzene solution. These compounds could be isolated after short reaction times, or they could be converted on continued heating to 2(5H)furanones, the product of intramolecular aldol condensation and... 

The importance of catalyst basic properties was emphasized by Malinowski et d They studied aldol condensation of formaldehyde with acetaldehyde, acetone, and acetonitrile. The rate constants for these reactions on Si02 mounted NaOH catalyst show correlation with NaOH content in the catalysts as shown in Fig. 4.37. Essentially the same linear relationship was observed for aldol condensation of acetaldehyde, and acetaldehyde with benzaldehyde. The linear relations support the view that basic properties are actually the cause of the catalytic activities. On Si02-supported NaOH catalysts, the groups - Si —ONa are assumed to be the active sites. 

P-Acetamido ketones. A three-component condensation involving a ketone, an aldehyde, and acetonitrile appears to involve aldol and Michael reactions and hydration of nitrilium species, which is quite unusual. 

The direct synthesis of a, unsaturated nitriles occurs in high yields at 40 to 50 °C from aldehydes and acetonitrile or benzyl cyanide in the presence of catalytic amounts of lb or 9b [125]. These reactions take place in both polar protic and non-polar aprotic solvents. Pro-azaphosphatrane 9b, which is a stronger base than lb, effidently catalyzes the condensation/dehydration of aromatic aldehydes and tertiary aliphatic aldehydes. The use of 9b in these reactions gave rise to products with imusuahy high E/Z ratios. With either lb or 9b, ahphatic aldehydes gave aldol products, and secondary aldehydes led to novel Michael addition products which are described in the next section. Ketones do not condense wiA either benzyl cyanide or acetonitrile under our conditions. 

Acetonitrile complexes of palladium have been shown to be effective catalysts for aldol-type condensation of methyl isocyanoacetate with benzaldehyde (Equation Mono- and diisonitrile Pd complexes were prepared and, as... 

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