摘要 : The availability of various types of formazans, the prospects for their use in the synthesis of heterocycles, and the principles of the construction of various heterocyclic systems on the basis of the formazan fragment have alread... 展开 The availability of various types of formazans, the prospects for their use in the synthesis of heterocycles, and the principles of the construction of various heterocyclic systems on the basis of the formazan fragment have already been discussed in general features in the first part of our review devoted to the synthesis of azoles on the formazans basis [1]. We will therefore only present a more detailed scheme of the possible paths to the formation of six-membered heterocyclic systems from formazans. As in the case of azoles, the principles of the construction of azine rings are based on the ability of the formazan fragment to enter completely or partially into the heterocycle that forms (Scheme 1) [2-11]. Most of the described paths (a-g in Scheme 1) involve intramolecular cyclization quite often without isolation of the precursor. There are only two examples of intermolecular [4+2] cycloaddition of formazans as 1,2,4-triazabuta-1,3-dienes with only one type of dienophile (path h) [12], since it has been demonstrated that the formation of 1,4-diaryl-3,6-bis(arylazo)-1,4-dihydro-1,2,4,5-tetrazines from 1,5-diaryl-3-chloroformazans (path i) is a two-step process and can be regarded as a variant of the intramolecular cyclization of path d (Scheme 1). 收起