Tandem Reactions of 2-Methylimidazoline and 1,2-Dimethylimidazoline with Various Benzoyl Chlorides

Abstract

The reactions of 2-methylimidazoline with excess benzoyl chlorides under mild conditions generated N,N¢-diacyl-b-keto cyclic ketene-N,N¢-acetals. Conversely, the corresponding reactions of 1,2-dimethylimidazoline under the same conditions stereoselectively formed the ring-opened (Z)-vinyl benzoates. The latter reactions feature the formation of carbon-carbon bonds, carbonnitrogen bonds, and carbon-oxygen bonds in one sequential cascade.

Reactions of Substituted Oxazoles and Thiazoles with Acid Chlorides: Carbon-Carbon Bond Formation through Cyclic Ketene Acetals

“…Recently, reactions of 2-methylimidazoline, 2-methyl-1,4,5,6-tetrahydropyrimidine, and 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine were reported to give various cyclic and acyclic products via cyclic ketene N,N¢-acetals when treated with aroyl chlorides in the presence of a base. [27][28][29] Also, 2-methylimidazoline, 2-methylimidazole, and 2-methylbenzimidazole formed both polycyclic and acyclic products with diacid chlorides through cyclic ketene acetal intermediates in the presence of a base. 30,31 Thus, we envisaged that analogous aromatic oxazoles and thiazoles with a 2-methyl group might undergo similar reactions with acid chlorides to those in Scheme 2.…”

Reactions of 2-Methyl- and 1,2-Dimethyl-1,4,5,6-tetrahydropyrimidine with Aroyl Chlorides: Diverse Reactivities of Cyclic Ketene N,N′-Acetals Generated in situ

“…8 Most recently, divergent reactions have been observed in the reactions of aroyl chlorides with 2-methyl-4,5-dihydro-1Himidazole (1) and 1,2-dimethyl-4,5-dihydro-1H-imidazole (2; Scheme 2). 9 Scheme 2 Divergent reactions of aroyl chlorides with 2-methyl-4,5dihydro-1H-imidazole (1) or 1,2-dimethyl-4,5-dihydro-1H-imidazole (2) This suggested that the N-substituents have a decisive effect on the reactivity of the five-membered ketene N,N¢acetals formed in these reactions. To investigate the effects of the ring size on the cyclic ketene N,N¢-acetals, we sought to expand this chemistry to the six-membered analogues of these compounds.…”

“…To investigate the effects of the ring size on the cyclic ketene N,N¢-acetals, we sought to expand this chemistry to the six-membered analogues of these compounds. We therefore examined the reactions of aroyl chlorides with 2-methyl-1,4,5,6-tetrahydropyrimidine (5) and 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine (9). The reaction of pyrimidine 5 with excess of an aroyl chloride in refluxing tetrahydrofuran-triethylamine mixtures did not generate the expected triaroylation product 7 (Table 2).…”

Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

“…Cyclic ketene acetals are a highly reactive class of compounds with significant synthetic potential [1]. The exocyclic methylene carbons in each are nucleophilic due to conjugation with the respective heteroatoms.…”

“…Pittman and coworkers have extensively explored the synthetic potential of many cyclic ketene acetal species [1,2] with both mono-and dielectrophiles, discovering a rich variety of reactions ranging from tandem cyclizations [1,3,4], bis additions followed by ring-opening and re-closure isomerizations [2], arylvinyl ester formation [1,4,5], ''push-pull'' compound formation [6,7], new heterocyclic ring and fused ring formation [2,3,6,8,9], ring-opening reactions [10], ring-retained polymerization and copolymerizations [11][12][13][14][15][16][17][18][19][20], spirobicyclic ring formation [21], and stereoselective radical cyclizations [21,22]. However, all of these studies have been carried out only on five-; six-; and seven-membered ring systems .…”