Spirocyclische 3‐Oxazoline durch 1,3‐dipolare Cycloaddition von Benzonitrilio‐2‐propanid mit 1,4‐Chinonen

Abstract

On irradiation with light of wavelength 290-350 nm, 2,2-dimethyl-3-phenyl-2 H-azirine (lb) reacts with 1,4-naphthoquinone to give the 1H-benzo Iflisoindol-4,9-dione (11) (Scheme 3) via cycloaddition of the benzonitrilio-2-propanide (2 b) onto the quinone C, C-double bond. With 2-methyl-and 2,3-dimethyI-l, 4-naphthoquinone, the nitrile ylide 2 b undergoes cycloaddition preferentially onto the C, 0-double bond of the quinone, leading to spiro-oxazolines 12 and 14 (Scheme 4 ) . Steric as well as electronic effects can be discussed to explain the observed site selectivity of the cycloaddition.With the 1,4-benzoquinones 15a, 15b, 15d and 15f, nitrile ylide 2b undergoes the 1,3-dipoIar cycloaddition exclusively onto the C, 0-double bond. The corresponding spiro-oxazolines have been isolated in 17-32% yield. This contrasts with the previously reported results with benzonitrilio-phenylmethanide (2 a), which undergoes cycloaddition to the C, C-double bond of 1,4-benzoquinones (cf. [ 11). This difference in the site selectivity of the 1,3-dipolar cycloaddition can be explained with Houk's concept of LUMO-polarization, that is, the stronger nucleophilic dipol2 b polarizes the LUMO of a a,P-unsaturated carbonyl compound more efficient than the less nucleophilic 2 a.This leads to a preference of the cycloaddition to the C,O-double bond in the case of 2b.With 2,3-dimethyI-(15c) and 2,3,5,6-tetramethyl-l, 4-benzoquinone (15e), nitrile ylide 2 b undergoes C, 0as well as C, C-cycloaddition (Schemes 7 and 8 ) .1. Einleitung. -Vor einiger Zeit haben wir uber photochemisch induzierte Cycloadditionen von 2,3-Diphenyl-2H-azirin (la) mit 1,4-Chinonen berichtet [ 11. Bei dieser Reaktion werden durch 1,3-dipolare Cycloadditionen des bei der Photolyse von l a ') *) Vorgetragen von H. H. an der Euchem-

Syntheses of 2H-1,3,2-Diazaphosphole, 2H-1,4,2-Diazaphosphole, and Δ3-1,3,2-Oxazaphospholene Complexes; First Examples of 2H-Azaphosphirene Complex Formation by [2+1] Cycloaddition

“…Selected spectroscopic data of 6 i ± k and 8 a ± g are given in Table 3 and Table 4, respectively. Related ambident [32] cycloaddition behavior of a-ketonitriles towards nitrilium betaines, such as nitrile ylides, [22] is well known.…”

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

“…For example, the more polar arylnitrile oxides and 1,4benzoquinones reacted via addition to the C=C bond to give fused isoxazole derivatives [10][11][12] as well as with the C=O bond yielding spirocyclic 1,4,2-dioxazole derivatives [13,14]. Furthermore, for photochemically generated benzonitrile isopropanide, competitive C=O and C=C additions with 1,4quinones were observed [15]. On the other hand, the slightly less polar benzonitrile benzylide underwent [3 + 2]-cycloaddition to the C=C bond exclusively [16].…”

Nitrile Ylides: Generation, Properties and Synthetic Applications

“…However, for 1,4-quinones, selective C,C or C,O double bond addition can be achieved depending on the substituents of the nitrile ylide. On the other hand, on irradiation of 2Hazirine 94 in the presence of 1,4-benzoquinones, the nitrile ylide undergoes the 1,3-dipolar cycloaddition onto the C,O double bond [108]. On the other hand, on irradiation of 2Hazirine 94 in the presence of 1,4-benzoquinones, the nitrile ylide undergoes the 1,3-dipolar cycloaddition onto the C,O double bond [108].…”