Kumulierte Ylide, XIV. Phosphacumulen‐Ylide als Cyclisierungsbausteine in der Heterocyclensynthese

Abstract

Es hat sich gezeigt, d& dieses Syntheseprinzip in weiten Grenzen zum Aufbau von 5-und 6-gliedrigen Heterocyclen angewendet werden kann, wobei die jeweilige Zwischenstufe 5 nicht isoliert wird. Entsprechend den fruher von uns erorterten stereoelektronischen Grunden nimmt die Reaktivitat von 1 gegenuber 4 von l a uber l b nach l c a b s .

E/Z Conformational equilibrium of N-substituted 2H-pyran-2-imines

“…Compounds 4 were found to exhibit at the NMR time scale E, Z-conformational equilibrium at the exocyclic C, N bond. Surprisingly, no experimental evidence for such equilibrium was provided by earlier reports on N-4,6-triphenylpyran 2-imine (4, R = R' = Ph) [2][3][4][5] or other pyran 2-imines 6,7 and benzoannelated analogs [8][9][10][11][12][13] . By contrast, the hindered rotation around C,N double bond in Naryl-2,6-dimethyl-4H-pyran-4-imines 5 and related iminium salts 6, 7 (Scheme 2) had been extensively investigated by 1 H, 13 C and 15 N NMR in the early eighties.…”

Novel Syntheses of α,β-Unsaturated Esters, α,β-Unsaturated γ-Lactones, and 2-Alkoxypyrroles via 1,2,4-Triazole-Stabilized Allenic Anions

“…3,4-Diphenyl- α , β -butenolide (16a): yield 67%; mp 151−153 °C; (lit . mp 149 °C); 1 H NMR δ 6.34 (d, 1 H, J = 1.6 Hz), 5.56 (d, 1 H, J = 1.5 Hz), 7.31−7.44 (m, 10 H); 13 C NMR δ 84.3, 114.6, 127.5, 127.8, 128.9, 129.1, 129.5, 129.6, 131.2, 134.9, 165.8.…”

Chemistry of Phosphorus Ylides, 11

“…These ylides have received remarkable interest by Bestmann [3], due to their wide applica tions for synthetic purposes. It was o f particular interest to investigate and compare the behaviour o f the reactive phosphacumulene ylides (2 ) and the stabilized phosphorus ylides (6 ) towards hy droxyxanthenone (1) and hydroxyquinoline M an nich bases (10,12).…”