Multicomponent‐Switched Reactions in Synthesis of Heterocycles

Dihydroazolopyrimidines: Past, Present and Perspectives in Synthesis, Green Chemistry and Drug Discovery

“…The difference between directions a and b suggests that the condensation of two carbonyl components cannot be the first step of reaction b and that the three-component treatment proceeds through the sequential interaction of the amine with two molecules of carbonyl compounds. This result is interesting because it is one of the first illustrations of the principle of so-called "multicomponent-switched reactions": the possibility of changing the reaction direction by moving from a stepwise interaction to a multicomponent interaction (more on this in ref [29] ). In such cases, the commutative property is not applicable and changing the order of addends does change the sum that also can be called as MCR effect.…”

“…Dihydropyrimidines anellated by an azole ring have been known since the 1980 s [11][12][13][14][15][16][17][18][19] and particular aspects of their chemistry have been described in several our reviews [20][21][22][23][24][25][26][27][28][29] and by other groups. [30,31] Since we are concerned with logical coherence, we considered it appropriate to provide a brief analysis of the most common result and only a few specific examples from previous work in this section of this review, therefore, most of the schemes in the section are of a general type.…”

“…This method never yielded isomeric structures like 5 (pathway b) and can be used to prepare dihydro derivatives of pyrazolo[1,5-a]-, imidazo[1,2-a]-, 1,2,3triazolo[1,5-a]-, 1,2,4-triazolo[1,5-a]-, tetrazolo[1,5a]pyrimidines, and pyrimido[1,2-a]benzimidazoles with di-verse substituents in both fused rings (see book and reviews). [20][21][22][23][24][25][26][27][28][29] In contrast to similar reactions of aminoazoles with βdiketones, this method of forming the pyrimidine ring exhibits higher regioselectivity. The established direction of cyclocondensation always corresponds to the first step of the reaction (alkylation of the aminoazole by the enone) with participation of the endocyclic reaction center and subsequent condensation of keto and amino groups (pathway a, Scheme 1).…”

“…The most important difference between such multicomponent reactions and cyclocondensation of aminoazoles with α,β-unsaturated carbonyls is realization of both possible directions a and b in formation of the pyrimidine ring: in some cases the isomeric compounds 4 and 5 can be obtained (both in mixture with other compounds and as a single product of the reaction). [20,[24][25][26][27][28][29] Moreover, the direction of the multicomponent reaction can often be controlled by varying the reaction parameters, which opens a way to tune the selectivity of such condensations (see detailed examples in Section 3).…”

Green multicomponent synthesis of pyrano[2,3-c]pyrazole derivatives: current insights and future directions

“…1,2 Among the myriad reactions and strategies in organic synthesis, the multicomponent synthesis of heterocyclic compounds holds a prominent position due to its efficiency and versatility. 3…”