Four-membered heterocycles, reviews

Aside from C-H coupling constants (often obtained from satellites in NMR spectra) not very much information is available on the NMR spectra of small heterocycles. A recent review (B-79MI50101) devotes only seven pages to the NMR spectra of all three- and four-membered heterocyclics. 

Tlie present chapter reviews the chemistry of three- and four-membered ring compounds containing an S—S bond in their ring. Dithiiranes 1,2-dithietanes and 1,2-dithietes are the compounds of this type. Although 1,3-dithietanes are four-membered heterocycles which are prepared much more easily and are seemingly more familiar, they have no S-S bond in the ring and hence are not included in this chapter. 

For a review on nonantiaromatic four- r-electron four-membered heterocycles, see Bertrand, G. Angew. Chem., Int Ed. Engl. 1998, 37, 270. 

A recent review on four-membered heterocycles formed from imino-phosphoranes concentrates on the preparation and the reactivity of 2,4-diimino-l,3-diazetidine and related compounds (93JPR305). As an example, the synthesis via bisiminophosphorane 85 is described in Scheme 42. The bisiminophosphorane has both a heteroaryl and a styryl site. From a mechanistic view, the reaction of the bisiminophosphorane proceeds with aryl isocyanate formation via an aza-Wittig mechanism. Intermediate car-bodiimide formation (86) occurs directly on the iminophosphorane moiety... 

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). 

One of the very few examples of a four-membered heterocycle with sulfur atoms substituted 1,2 was reported by Dupont workers (60JA1515,61JA3434). Its synthesis involves the high temperature reaction of fluorinated alkynes and elemental sulfur, probably via a diradical intermediate (Scheme 102). The chemistry of these 1,2-dithietenes has been reviewed (76RCR639). As discussed later, these dithietenes form complexes with a number of transition metals. 

A review of the formation of four-membered heterocycles through electrophilic heteroatom cyclisation is available <02EJ03099>. 

Among the four-membered heterocycles, 2-azetidinones have received considerable attention due to the presence of a -lactam ring as an important structural feature for the biological activity of penicillins, cephalosporins and related antibiotics.Recent reviews of B-lactam syntheses have been given by Sammes, Isaacs, Mukerjee, Hegedus, Labia and Barrett. The most complete and exhaustive ac-... 

Reviews on the following aspects of four-membered heterocycles have appeared 1,2-dioxetans and the reaction of singlet oxygen with alkenes/ /8-lactam antibiotics, small ring compounds of sulphur and selenium," recent developments in the synthesis of azetidines, the chemistry of benzazetes and of thiacyclobutenes (thietes) and their valence tautomers, and conformational barriers and interconversion pathways in some small ring systems. ... 

The chemistry of organic isocyanates, including a number of routes to four-membered heterocycles, has been reviewed. ... 

Review Muller, L. L. Hamer, J. 1,2-Cycloadditions The Formation of Three- and Four-Membered Heterocycles-, Wiley New York, 1967. 

The reader is referred to previous reviews for historical aspects and early work. For condensed quinazoline systems, The Chemistry of Heterocyclic Compoundsr—Six Membered Heterocyclic Nitrogen Compounds with Four Condensed Rings should be consulted. 

Volume 59 consists of four chapters. The first is by M. J. Silvester (Aldrich Chemical Co. Ltd.), and deals with polyfluoroheterocycles, updating the review by Chambers and Sargent which appeared in Volume 28 of Advances in Heterocyclic Chemistry in 1981. It covers mainly six-membered ring heterocycles and complements a review by Burger that will appear in Volume 60 of our series and will cover fluorine-containing five-membered heterocyclic rings. 

A review which includes the formation of four-membered rings among a range of other heterocycles has appeared <99MI637>. 

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