Allyl azides, photolysis

Irradiation of allyl azide produced the imine of acrolein but photolysis of l-azido-2-phenylprop-2-ene (63) in cyclohexane solution resulted in a small yield of the azacyclobutane (64) and 2-phenyl-propenalimine (65) . This is the first observation of an 1-azabi-cyclo [1.1.0]-butane ring in the products of photodecomposition of an allylic azide. 

Alkenyl and allyl azides give nitrenes, which undergo intramolecular addition to give highly strained compounds (Scheme 6.20). Conversely, addition of triplet (radical) traps such as dienes or a-methylstyrene increases the stereospecificity by selective removal of the triplet. Photolysis is less stereospedfic since a higher percentage of the nitrenes is generated directly as triplets. 

Tridentate salen ligands (10) derived from 1 have given excellent results in the enantiocontrol of the hetero Diels-Alder addition reaction of dienes with aldehydes (eq 7) and in the asymmetric additions of TMS-azide to mc5o-epoxide and trimethylsilyl cyanide to benzaldehyde (up to 85% ee). Phosphino-oxazolines derived from 1 have been employed for the asymmetric control of palladium-catalyzed allylic substitution reactions products of 70-90% ee were obtained. Photolysis of crystalline adducts of enantiomerically pure 1 with prochiral alcohols results in asymmetric inductions of up to 79% in a rare example of a solid-state enantioselective reaction. ... 

Photolysis of pivaloyl azide in cyclohexene produces 41% isocyanate, 45% JV-pivaloylaziridine (108), T5% of the allylic amide (109), a trace of bi(cyclohex-2-enyl) (110) and some pivalamide (111). 

The insertion of nitrenes, generated via the photolysis or thermolysis of azides, into C-H bonds is well known, although the yields are generally poor. However, when ethyl azidoformate is thermolyzed in the presence of 1-chlorocyclohexene, the allylic insertion product is formed in 49% 3deld (eq 10). In this case it is not clear if the product is formed through direct insertion or by the ring opening of an aziridine intermediate. 

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