Additionsreaktionen von 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirin an Phenylisocyanat und Diphenylketen

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Abstract
Addition Reaction of 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine with Phenylisocyanate and Diphenylketene3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine (1a) reacts with carbon disulfide and isothiocyanates with splitting of the azirine N(1), C(3)‐double bond to give dipolar, fivemembered heterocyclic 1:1 adducts. In some cases, these products can undergo secondary reactions to yield 1:2 and 1:3 adducts. In this paper it is shown that the reaction of 1a with phenylisocyanate also takes place by cleavage of the N(1), C(3)‐bond, whereas with diphenylketene N(1), C(2)‐splitting is observed.The reaction of 1a and phenylisocyanate in hexane at room temperature yields the 1:3 adduct 2 in addition to the trimeric isocyanate 3 (Scheme 1). A mechanism for the formation of 2 is given in Scheme 5. Hydrolysis experiments with the 1:3 adduct 2, yielding the hydantoins 4–6 and the ureas 7 and 8 (Schemes 3 and 5), show that the formation of this adduct via the intermediates d, e and f is a reversible reaction.The aminoazirines 1a and 1b undergo an addition reaction with diphenylketene to give the 3‐oxazolines 14 (Scheme 8), the structure of which has been established by spectral data and oxidative degradation of 14a to the 3‐oxazolin‐2‐one 15 (R1  R2  CH3, Scheme 9).

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