2-Cyanoacrylates as reagents in heteroatomic synthesis (a review)^†

Several types of addition reactions to the CC bond of alkyl 2-cyanoacrylates, CH₂C(CN)COOR (1), are considered. The first examples deal with addition of CH-Acids (pK_a less than 13) and of H₂S in the presence of catalytic amounts of strong amines, also of mercaptans, thiocarboxylic, and thiophosphoric acids. P-Sulfenylchlorides and acidic phosphites add irreversibly at 20°C to form addition products in accordance with the distribution of charges in 1. HCl reversibly adds to 1 and to the acid chloride CH₂C(CN)COCl (2). Alcohols and H₂O also add reversibly to the acid CH₂C(CN)COOH (3) and to esters of 1 to transform 1 and 3 into polymers. Triethylsilane in the presence of CF₃COOH (4) reduces the CC bond of 1 and 3 to the corresponding saturated derivatives.

The second set of examples involves reactions of 1 with P-III compounds in the presence or absence of 4. Ph₃P as well as other weak nucleophiles reversibly add to 1 in the absence of 4 to cause instant polymerization. However, 4 protonates an initially formed zwitter-ion in the reaction of 1 with Ph₃P,(EtO)₂PCl,Ph₂PCl and thiourea to afford stable addition products. IR spectroscopy reveals the formation of H-complexes of 4 with the CN and COOR groups of 1, which stimulates the addition of the weak nucleophile (o-C₆H₄O₂)PCl to the CC bond of 1. This reagent does not react with 1 in the absence of 4. Strong nucleophiles, Alk₃P, and (Et₂N)₃P in excess irreversibly add at 20°C to 1 to form zwitterions, which specifically react with PhNCO to give stable products. 1,3,2-Dioxaphospholes react with 1 either to form spirophosphoranes or 2-cyano-3-phosphoranylpropionates.