Zum Mechanismus der Photochemie des Benzfurazans

Abstract

Mechanistic studies on the photochemical reactions of benzfurazan. From other works it is known that irradiation of benzfurazan (1) in methanol gives the carbaminacid‐ester 4, whereas in benzene the azepinederivative 3 is obtained (Scheme 1). The compounds 5–8 (Scheme 2) have been proposed as intermediates. In our investigations we detected and characterized by means of UV.‐ and IR.‐spectroscopy the two species 5 and 8. Irradiation of 1 with 350 nm light at room temperature in a strongly polar solvent (e.g. H2O) yields exclusively 5 (Fig. 1) with a quantum yield of 0.48. In non polar solvents (e.g. hexane) 5 isomerizes in a second photochemical step to 8 (quantum yield 0.43) (Fig. 3). Thermally, 5 can be converted back to 1. The rate constant for this reaction at room temperature is 2 · 10–5s–1. The transformation 5 → 8 was also investigated at low temperature. There was no direct evidence for any intermediates of the type oxazirene (6) or nitrene (7). However, the formation of azepine 3 upon irradiation of 5 in benzene suggests as intermediate the nitrene 7 which could be converted into 8 in a fast thermal reaction (Scheme 3).

Dihydropyridine receptor of L-type Ca2+ channels: identification of binding domains for [3H](+)-PN200-110 and [3H]azidopine within the alpha 1 subunit.

“…Both probes could therefore specifically label regions near, but not directly involved in, the formation of the DHP binding domain. We therefore also studied the peptide fragments photolabeled by the optically pure DHP (+)-PN200-110, which contains a photoreactive benzofurazane group (13) at the para position of the DHP ring near the binding center of the molecule. Diazipine, azidopine, and (+)-PN200-110 all photolabeled the same endoproteinase Lys-C fragments in domain III (-50M of the total photolabeling) and domain IV [-30% for diazipine and azidopine; -15% for (+)-PN200-110].…”

Oxadiazoles

“…For example, benzofurazan 446 in benzene affords cyanoisocyanate 498 and azepine 499 (Scheme 13.171). Compound 499 probably originates from the reaction of the solvent with the acylnitrene intermediate 497 [443].…”

A Rearrangement of 3-Pyrazolines as a Missing Link

“…However, many photorearrangements of substituted indazoles [14], imidazoles [15], oxazoles [16], thiazoles [17], and thiophenes [18] are more complex and require additional steps.…”