Diazetidine

the preparation of the parent compound has, as yet, not been achieved. However, numerous 1,2-diazetidines are known. 

The standard synthesis is a [2+2] cycloaddition of electron-rich alkenes such as enol ethers or enamines to azo compounds, e.g.  

2-Diazetidines and l,2-diazetidin-3-ones are thermally very stable. On strong heating, they decompose either into an azo compound and an alkene or ketene, or into two molecules of imine or an imine and isocyanate. 

By analogy with y -lactams, l,2-diazetidin-3-ones react with nucleophiles with ring-opening, e.g.  

The (2 + 2)-cycloaddition of ketenes to azo compounds yields l,2-diazetidin-3-ones, for example  

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Diazetidine-3,4-dione, 1,2-di-t-butyl-electrophilic reactions, 7, 460 spectroscopy, 7, 454... 

Diazetidines applications, 7, 483 electrophilic reaction, 7, 460 nitrogen inversion, 7, 10 nucleophilic reactions, 7, 462 photochemical reactions, 7, 456-457 reductive cleavage, 7, 465 spectroscopy, 7, 451-454 structure, 7, 451... 

Making use of the same reaction principle, disubstituted ketenes 66 have been reacted with aldehydes 80 to form p-lactones 81 [100], with diazo-compounds 82 to form 1,2-diazetidin-3-ones 83 [101] and with nitroso-compounds 84 to form 1,2-oxazetidin-3-ones 85 as precursors of a-hydroxy carboxylic acids (Fig. 42) [102],... 

Indene, however, does give four-membered ring adducts with PTAD,69 and phthalazine-t,4-dione.70 The reaction with PTAD proceeds stepwise via the dipolar intermediate 43, which was trapped in the presence of water to give 44, under conditions in which the 1,2-diazetidine (45) was not opened by water to 44 (Scheme 5).69 Hydrolytic cleavage of the triazole ring in 45 using potassium rm-butoxide in wet dimethyl sulfoxide, followed by... 

Carbocyclic compounds containing an unsubstituted exocyclic methylene group give 1,2-diazetidines with PTAD. Methylene adamantane gives the adduct 47,8 5 and the methylene cyclopropane (48, R = H) gave the 1,2-diazetidine 49.86 The phenyl-substituted compound (48, R = Ph) behaved similarly to styrene and gave a 2 1 adduct with PTAD (see Section IV,D,1). 

A 1,2-diazetidine has been proposed as an intermediate in the reaction of pyridazine-3,6-dione (12) with styrene.87 The observed product was thought to arise from addition of water to the 1,2-diazetidine, although the alternative more likely explanation involving a dipolar intermediate (cf. Scheme 5) was apparently not considered. In the photochemical reaction of styrene with DEAZD, a 1,2-diazetidine structure was tentatively assigned to a minor product.88 Attempted photochemical [2 + 2] cycloaddition of DEAZD to other olefins failed to give any 1,2-diazetidines.88... 

In the reaction of the cis-disubstituted olefins 53 (X = S, R = Me) and 53 (X = O, R = D) with DMAZD, only the cis- 1,2-diazetidines are formed.94,95 The observation of this stereospecificity, the isotope effects and lack of solvent dependence would seem to support a concerted mechanism, although the workers prefer to explain the isotope effects by a stepwise mechanism involving a dipolar intermediate, similar to that already described for the reaction of PTAD with indene.95 Other workers claim that the reaction is... 

ADC compounds add to allenes to give 3-methylene-1,2-diazetidines. Tetramethoxyallene adds to DEAZD and to PTAD to give adducts 59 and 60 in 43 and 69% yield.99 DEAZD adds to the 2,3-double bond of 1,1-difluoroallene (in poor yield), in contrast to maleic anhydride which adds to the 1,2-double bond.100 o... 

Aliphatic azo compounds usually undergo photoextrusion of nitrogen (cf. chapter 2.3.3). Nevertheless 1,2-diazetidines are formed efficiently when there is a favourable interaction between the pi-systems of the N—N and the C-C bonds (4.85)499). 

The most surprising aspect is the number of rings that are planar or nearly so. The notable exceptions are the 1,2-diazetidine, the 1,2-dioxetane and the 1,2-oxathietane oxide rings. However, the reason for lack of planarity is not clear. 

Electrophilic Attack on Ring Heteroatoms 5.15.2.2.1 1,2-Diazetidine derivatives... 

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