Photochemie von Acylaziden. VIII [1]. Reagieren Acylnitrene wie 1,3-Dipole??

Abstract

Photochemistry of Acylazides. VIII. Do Acylnitrenes React like 1,3‐Dipoles? The formation of three‐ ore five‐membered heterocyclic rings by the reaction of acylnitrenes with olefins depends on the electron density at the double bond. The generally expected formation of aziridines by a cheletropic reaction was observed by photolysis of aroylazides 1 in the presence of 2,5‐dihydrofuran 2. But with enolethers 3 and 4 oxazolines were directly formed. This [3 + 2] cycloaddition is regiospecific. The cycloaddition is modestly stereoselective by steric hindrance within the cyclic enolether 3b. Very small de‐values were found with chiral substituents in the acylazide 13. The azide decomposition was also achieved by photoinduced electron transfer. The same cycloaddition products as obtained by direct photolysis of the azides were obtained via radical anions of the acylazide. Using Michler's ketone as electron donor in the triplet state the formation of isocyanate which diminishes the yield of cycloadducts can be avoided.

Small Rings by Azide Chemistry

“…41 Similarly p -cyanobenzoylnitrene, when generated by photolysis of the azide 21 in the presence of 2,5 -dihydrofuran, gives the aziridine 22 in moderate yield (Scheme 6.11 ). 42 This nitrene and other p -substituted benzoylnitrenes also react with C 60 to give fulleroaziridines such as 23 . 43 Scheme 6.10 Alternative mechanisms for the formation of aziridines from alkenes and organic azides 39…”

“…49 Furthermore aziridine diesters are generated from some α , β -unsaturated esters. 50 Even octafl uoronaphthalene reacts with ethyl azidoformate to give an aziridine (although Scheme 6.11 Cycloaddition reactions of photochemically generated p -cyanobenzoylnitrene 42 this might be via a triazoline intermediate). 51 An aziridine was isolated in good yield from the reaction of ethoxycarbonylnitrene with 1,2 -dimethylcyclobutene, but the corresponding reaction with 1 -methylcyclopropene led only to an acyclic product 52 .…”

Cycloaddition Reactions of 1,3-Diaza-2-azoniaallene Salts and Glycals

“…For 13a couplings 3 J 2',3' of 6.2 Hz and 3 J 3',4' of 4.3 and 10.1 Hz were observed, which are in accordance with a trans configuration [21]. A rationale for the formation of these compounds is given in Scheme 8.…”

“…[C 21 [28], routine MULABS, µ = 18.06 cm -1 , 0.65 -0.90 transmission); 63444 reflections; 7758 independent reflections (R int = 0.0808). The structure was solved by the Patterson method (program DIRDIF) [34] and refined using the program SHELXL97 [35] against F 2 of all reflections.…”

“…Acyl nitrenes produced photochemically from acyl azides have been reported to undergo 1,3-dipolar cycloaddition to the double bond of dihydropyran [21].…”