Photochemische Cycloadditionen von 3‐phenyl‐2h‐azirinen mit Aldehyden. 31. Mitteilung über Photoreaktionen

Abstract

Experiments concerning the photochemical condensation of 3-phenyl-2 H-azirines 1 with aliphatic and aromatic aldehydes to 3-oxazolines 4 are fully described (cf. scheme 1). Photochemically nitrile methylides of type 2 are first formed, which then very quickly react thermally with the aldehydes in a regiospecific manner to give the 3-oxazolines 4. Azirines monosubstituted in position 2 ( l b and Ic) give mixtures of cis, trans-oxazoline isomers, in which the cis isomer predominates. The stereoselectivity of the cycloaddition reaction can be rationalized by a simple model (scheme 10).The stereoisomeric 3-oxazolines 4 are distinguishable in the NMR. spectra by the large homoallylic coupling constants between the H atoms on C(2) and C(5) 1. Einleitung. -In einer vorlaufigen Mitteilung [2] berichteten wir vor kurzem uber die Bildung von 3-Oxazolinen 4 bei der Bestrahlung von 3-Phenyl-2 H-azirinen I) 30.Mitteilung siehe [l].

Interproton spin-spin coupling across a dual path in 2,5-dihydrofurans and phthalans

“…Results for compounds 8-10 are typical. 23 It can be seen that both values of 72.5 in 8, which should exist in an average conformation very similar to 2,3-diphenyl-2,5-dihydrofuran (4), are in fact almost identical with those shown in Table I, but 72,5 in the cis isomer 10 where the steric repulsion between the cisphenyl groups at C2 and Cs becomes severe is considerably elevated.…”

Proton nuclear magnetic resonance spectra of cyclic monoenes: hydrocarbons, ketones, heterocycles, and benzo derivatives

“…A later, more accurate analysis of 64a,b (R = COCH3) confirmed the earlier results with slightly different numerical values. 208 In what appears to be the latest study of the 2,5-dihydrofuran system (61) complete iterative analyses-including sign determination-for 2-methoxycarbonyl-61, 2,3-diphenyl-61, and for five derivatives of phthalan (65) were reported. 207 The data 65 for the first two compounds are included in Table X.…”

Photochemistry of the carbon-nitrogen double bond

“…325 In this case, the methylene chain is sufficiently long to In a somewhat related case, Schmid and co-workers reported on the photoisomerization of dihydroisoxazole 314 to dihydrooxazole 3 1 7. 288 The reaction was proposed to proceed via a transient azirine (315). This intermediate was not isolated but was suggested to undergo rapid ring opening to nitrile ylide 316 which cyclized to the observed photoproduct via an internal 1,3-dipolar cycloaddition reaction.…”