Oxidative (3+3) Cycloaddition/Ring-Opening Reactions of Simple Urea Derivatives and N,N′-Cyclic Azomethine Imines to Construct 1,2,3,5-Tetrazine-4(1H)-one Derivatives

Abstract

A novel oxidative (3 + 3) cycloaddition/ring-opening reaction of N,N′-cyclic azomethine imines with the in situ generated diaza-oxylallyl cations from simple urea derivatives in the presence of base and PhI(OAc)2 has been developed. This transformation performs well over a broad substrate scope, which provides facile and rapid access to 1,2,3,5-tetrazine-4(1H)-one derivatives in good yields.

Diastereoselective Synthesis of Pyrazolo[1,2‐a][1,2,4]triazine Derivatives via Cross‐1,3‐dipolar Cyclizations of Azaoxyallyl Cations with N,N′‐Cyclic Azomethine Imines

“…[8] Very recently, our group disclosed an oxidative cycloaddition/ringopening reaction of N,N'-cyclic azomethine imines with simple urea derivatives for the synthesis of 1,2,3,5-tetrazine-4(1H)-one derivatives. [9] On the other hand, the azaoxyallyl cations which can be generally in situ generated from α-halohydroxamates in the presence of bases were also used as versatile surrogates of "1,3dipole", [10] and a series of [3 + 1], [11] [3 + 2], [12] [3 + 3], [13] [3 + 4] [14] cycloaddition reactions involving azaoxyallyl cations have been developed, in these reactions, sulfur ylides was employed as one-atom synthons, 2π systems and 4π systems were employed as two-atom and four-atom units respectively. Especially, other 1,3-dipoles such as isoquinoline N-oxides and nitrones were successfully explored as three atom cycloadditon partners with azaoxyallyl cations in the [3 + 3] cycloadditions by several groups.…”