Heterocycles with four heteroatoms reviews

No single chapter in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I) was devoted to 6,6-fused heterocycles containing four heteroatoms arranged 1 3 with no heteroatoms occupying the bridgehead position. Indeed, the ring index of that edition only contained one example and subsequent reviews have referred to just one other <93PHC256>. This chapter describes such 6,6-... 

The present review is concerned with four-membered heterocycles that contain one sulfur atom either alone or associated with another heteroatom. The classes of compounds that will be discussed are the thietanes (1) and thietes (2), the 1,2-oxathietanes (3), the / -sultines and -sultones (4 and 5), the 1,2- and 1,3-thiazetidines (6 and 7) and thiazetes (8), the 1,2- and 1,3-thia-phosphetanes (9 and 10), and the 1,3-silathietanes and 1,3-selenathietanes (11 and 12). 

The compounds with five-membered rings containing three or four heteroatoms including at least one phosphorus were first systematically reviewed in Chapter 4.22 of CHEC-II(1996) by Schmidpeter <1996CHEC-II(4)771>. In CHEC(1984), only few examples of 2//4,2,3-diazaphospholcs were mentioned in the general chapter on phosphorus heterocycles <1984CHEC(1)493>. 

The chemistry of cyclopentafurazans (cyclopen-ta-1,2,5-oxadiazoles) and furazans fused to five-membered heterocycles with one to four heteroatoms has been reviewed (95JHC371). Treatment of 3-amino-4-nitro-l,2,5-oxadiazole with dinitrogen pentoxide yields dinitro-1,2,5-oxadiazole 89 (95MC102). The latter reacts normally with benzenethiol to give the sulfide 90,... 

There are several reviews, which are devoted to the synthesis of seven-membered heterocycles, but rings with four or more heteroatoms are not typically described in these reviews <888569,9isi8i>. Only a few of the possible heterocyclic structures are actually known most contain nitrogen and... 

Abstract This chapter is devoted to recent progress in the chemistry of the 5 5 fused heterocyclic systems. There are four possible modes of 5 5 fusions of the simple five-membered heterocycles leading to four structures containing one heteroatom in each ring. The heteroatoms may be the same or different and may be O, NH, S, Se, Te, P, As, or Sb. The fully conjugated hetero analogs of pentalene dianion have a central C-C bond and are isoelectronic with the 10-7t-electron pentalene dianion. The scope of the chapter is outlined with a survey of various structural types and nomenclature of the parent compounds and their derivatives. New synthetic procedures and synthetic applications of title compounds are presented. This review has concentrated on the new developments achieved from 1997 to September 2007. 

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