Heterocyclics 1.2- diazetidines

Conversion of other heterocyclic systems into pyridazines has also been used, for example the reaction of 3-aminopyrone 9 with hydrazine, followed by oxidative aromatisation <06T9718> and the more unusual utilisation of a 1,2,4-triazole 10 as the source of the N-N unit <06T8966>. In this latter transformation, the intermediate quaternary salt 11 was isolable. An even more unusual example was the reaction of the diazetidine 12 with enolates <06S2885>. 

Hassner A (ed) (1984) Azetidines, /J-lactams, diazetidines, and diazirines. Small ring heterocycles. Part 2, The chemistry of heterocyclic compounds. Interscience, New York, p 589... 

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... 

Four-membered heterocycles containing more than one heteroatom Dithietanes, dithietes, diazetidines... 

Formation of Four-membered from Six-membered Heterocycles 5.15.3.8.1 1,2-Diazetidine derivatives... 

Diazetidines. A saturated four-membered ring containing two adjacent nitrogen atoms is named a 1,2-diazetidine 1. When the two nitrogen atoms and the two carbon atoms are alternatively present in the four-membered ring, it is named a 1,3-diazetidine 2, which is also known as uretidine. Fused multinuclear heterocyclic systems are known as diazacyclobutane derivatives. For example, 3,4-benzo-l,2-diazetidine is referred to as l,2-diaza-3,4-benzocyclobutane 3. 

Su and Chu <1999CPL(308)283> have also carried out B3LYP/6-31G level calculations for 1,3-diazetidine, especially for carbene generation from this heterocycle. The carbene generated from 1,3-diazetidine is a 4k electron system. The relative energies of carbene 21 are summarized. 

Unlike cyclobutane and its derivatives, many of the four-membered heterocycles usually have planar structures. However, diazetidines are slightly nonplanar or puckered. Earlier, Ruben and co-workers <1974AXB1631> and Loeppky et al. <1991JA2308> have reported X-ray crystallography of a few 1,2-diazetidines. Beckert and co-workers <2002H(57)1257>, while carrying out cyclization of amidrazone with bis-imidoyl chloride, isolated a new crystalline compound which was not the expected triazine but A2-l,2-diazetine or 1/7,4/7-diazetine derivative 22 as established by X-ray analysis. 

Four-membered heterocycles with two nitrogen atoms are widely used in research and industry. Numerous examples of 1,3-diazetidines are extensively used in the polymer industries. 

The 15CH coupling constants (often obtained from 13C satellites in H NMR spectra) of small heterocycles have been listed <1979MI50101>. A 13C NMR study of 1,2-dimcthyl-3-/W/-butyldiaziridinc showed that the population of the 1,2-cis isomer increases with solvent polarity (see Section 2.5.3.8) <1998MC113>. 13C Chemical shifts for the ring carbons of representative derivatives of dithiiranes , azetidines , diazetidines , thiazetidines , dioxetanes , and 1,2-oxathietane S,A-dioxides (-sultones) have been tabulated. 

Nitrogen substituted carbodiimides are usually not stable in the carbodiimide configuration. Some derivatives can be distilled under vacuum, but on standing they undergo slow dimerization reactions. In one case of N-heterocyclic carbodiimides the 1,3-diazetidine diimine dimers are obtained instead of the monomers. Semiempirical calculations on the formation of 1,3-diazetidine diimine dimers of H2N—N=C=NMe confirm the Z,Z and E,E configurations of the dimers obtained. N-nitrosubstituted carbodiimides are more stable. 

Molina, P., Alajarin, M., Lopez-Leonardo, C., Elguero, J. Four-membered heterocyclic rings from iminophosphoranes. Preparation and reactivity of 2,4-dimino-1,3-diazetidines and related compounds. J. Prakt. ChemJChem.-Ztg. 1993, 335, 305-315. 

Chemical activities and biological applications of diazetidines, furoxans, triazoloi-mines, guanidines and other heterocycles as nitric oxide donors 02CRV1091. 

The Wittig-type reactions of iminophosphoranes with isocyanates and related compounds have also been extensively used in heterocyclic synthesis. Examples include the preparations of the mesoionic [l,3,4]thiadiazolo[2,3-c][l,2,4]triazines (210) from (209), 0 bicyclic guanidines, e.g. (212), from (211), naphthypyridines (215), (216), and (217) from (213) and (214), 2 pyrido[l,2-f]pyrimido-[4,5-d)pyrimidines (218), 7H-pyrido-[4,3-c]- (219) and 10H-pyrido[3,4-b]- (220) carbazoles, tricyclic fused 2,4-diimino-l,3-diazetidines (222) from the bisiminophosphorane (221), benzotriazepines (225) from (223) and (224), 6 and mesoionic thiazolo-[2,3-b]-1,3,4-thiadiazoles (227) and N,N-bisheteroarylamines from the iminophosphorane (226), derived from 3-amino-4-phenylthiazole-2(3H)-thione. The carbodiimides (229), prepared from the iminophosphorane (228), can be converted into quinolines or a-carboline derivatives depending on the nature of the isocyanate used in the reaction with (228) and the reactions of iminophosphoranes (230) and (231) with aryl and styryl isocyanates provide one-pot syntheses of quinoline, a-carboline, and quinindoline derivatives. 9... 

A. Hassner, J. A. Moore, R. S. Ayers, G. A. Koppel, R. Richter, H. Ulrich, and H. W. Heine, Small Ring Heterocycles. Part Two. Azetidines, Lactams, Diazetidines, and Diaziridines, 1983. 

For reviews on the synthesis of p-lactams, see a) Sheehan JC, Corey EJ (1957) Org Reac 9 Chapt 6 b) Mukerjee AK, Srivastava, RC Synthesis 1973 373 b) Isaacs NS (1976) Chem Soc Rev 76 181 c) Bose AK, Manhas MS (1976) Lect Heterocycl Chem 3 43 d) Mukerjee AK, Singh AK (1978) Tetrahedron 34 1731 e) Koppel GA (1983) In Hassner A (ed) Small ring heterocycles-azetidines, p-lactams, diazetidines and diaziridines, Wiley, New York, Chapt 2 f) From azetidiniminium salts, see Ghosez L, Bogdan S, Ceresiat M, Frydrych C, Brynaert J, Portuguez MM, Huber I (1987) Pure Appl Chem 59 393... 

A soln. of diphenylketene p-tolylimine and azobenzene in anhydrous ether refluxed at least 4 days under a sun lamp l,2,4,4-tetraphenyl-3-p-tolylimino-1,2-diazetidine. Y 83%. F. e. s. M. W. Barker and M. E. Goker, J. Heterocyclic Ghem. 4, 155 (1967). 

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