Environmentally safe one-pot solvent-free synthesis of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) catalyzed by NaHSO4-SiO2

Abstract

One-pot condensation of thiourea (urea), diverse aromatic aldehydes, and ammonium acetate in the presence of repeatedly usable heterogeneous catalyst NaHSO 4 -SiO 2 in the absence of solvent under the microwave irradiation proceeds faster and with better yields of 6-aryl-1,2,4,5-tetrazinane-3-thiones(ones) that under common heating. Compounds synthesized exist as a rule as two isomers distinguished by the position of the phenyl ring: It is located in the major isomer nearly in the equatorial position, in the minor one, close to axial position.

Homogeneous and heterogeneous catalysts for multicomponent reactions

“…332 The formation of N-N bonds is not easy and 1,2,4,5-tetrazines have generally been prepared from hydrazine derivatives or from nitrilimines. 331 Recently Gopalakrishnan et al 333 bases (Et3N, Et2NH). 358 When reaction is performed under classical conditions, the reaction product resulting from this cycloaddition possesses two asymmetric centres and is therefore capable of existing as a mixture of cis-and trans-diastereoisomers, being the cis compound the main product.…”

Diversity Oriented Syntheses of Conventional Heterocycles by Smart Multi Component Reactions (MCRs) of the Last Decade

“…This will be of course supported by a high ratio of liquid components and their suitable properties. Several syntheses have been carried out with neat components, and detailed studies on this issue have been done in sub-sections 2.4 [ 33 , 34 ], 2.11 [ 59 ], 2.17 [ 74 ], 2.19 [ 79 ], and 2.24 [ 92 ].…”

“…In a 3CR benzaldehyde aminoacetal 56 is formed. A sequence of metathesis reactions connect the amino functions of both 56 and urea together forming 6-aryl-1,2,4,5-tetrazinane-3-one 57 in good yields of 68–80% [ 92 ]. Two equivalents of hydrogen are released ( Scheme 25 ).…”

Acyclic and Cyclic Ureas (Update 2013)

“…[187] A one-pot condensation of urea, aromatic aldehydes, and ammonium acetate in the presence of catalytic amounts of sodium hydrogen sulfate/silica gel in the absence of solvent and under microwave irradiation has been claimed to yield 6-aryl-1,2,4,5-tetrazinan-3-ones. [188] Scheme 66 Formation of N3-Substituted 3,4-Dihydropyrimidin-2(1H)-ones from a Phosphonate, a Nitrile, an Aldehyde, and an Isocyanate [185,186] …”