cis‐/trans ‐[1.1.1]‐O,N,C‐Tris‐σ‐homobenzole — Synthesen, [ _σ 2 + _σ 2 + _σ 2]‐Cycloreversionen, O,N‐Heteronine

Abstract

Für die cis‐O,O,N‐Tris‐σ‐homobenzole 1a,b wurden drei alternative Synthesen, letztlich ausgehend von Benzol oder p‐Chinon, entwickelt. Für eines dieser Verfahren wurde die radikalische Bromierung von (Tosylimino)‐1,4‐cyclohexadien und die Äquilibrierung bzw. Trennung der daraus resultierenden Mono‐ bzw. Dibromide untersucht. Zwischenprodukte der Synthesen wurden für die Herstellung der trans‐O,O,N‐Tris‐σ‐homobenzole 6/7 verwendet. Der für die cis‐O,N,N‐Verbindung 2a entwickelte Zugang basiert auf cis‐Benzoldioxid (11). cis‐/trans‐N,N,C‐ (3a, b/9a und cis‐/trans‐O,N,C‐Tris‐σ‐homobenzole (5a, b/10a, b) wurden über CH2N2‐Addition an cis‐N,N‐ bzw. cis‐N,O‐Bis‐σ‐homobenzole zugänglich. Ein effizienter Zugang zu cis‐N,N,C‐Gerüsten (3) geht von gut zugänglichen cis‐O,O,C‐Verbindungen (51) aus. Letztere sind auch Edukte für cis‐S,S,C‐Tris‐σ‐homobenzole (4). Die cis‐Tris‐homobenzole 1a,b (1b: ΔH≠ = 37.1 ± 2.1 kcal/mol, ΔS≠ = 4.1 ± 4.4 e.u.), 2 (2a, ΔG≠ = 33.7 kcal/mol), 3a,b (3a: ΔG≠ = 28.6 kcal/mol; 3b: ΔH≠ = 29.5 ± 1.1 kcal/mol, ΔS≠ = −2.4 ± 2.7 e.u.) und 5a,b (5b: ΔG≠ = 30.2 kcal/mol) gehen die thermische [σ2 + σ2 + σ2]‐Cycloreversion zu den jeweiligen O,N‐Heteroninen ein. Die Aktivierungsbarrieren sind im Einklang mit einer kooperativen 3σ→3π‐Isomerisierung. Für das 4,7‐Dihydro‐1,4,7‐oxadiazonin 67a ist durch Röntgenstrukturanalyse eine verdrillte Bootkonformation ausgewiesen.

Chiral lithium amide base-mediated rearrangement of meso-cyclohexene oxides: asymmetric synthesis of amino- and aziridinocyclohexenols

“…The combined organic extracts were dried (MgSO 4 ) and evaporated at room temperature under reduced pressure to give the crude product. Purification by Kugelrohr distillation gave aziridine 8 (730 mg, 88%) as a colourless oil, bp 60-80 ЊC/10 mmHg (lit., 23 60.5-61.5 ЊC/14 mmHg); data identical to those reported previously. 23 Aziridine 8 should be used immediately or stored under nitrogen in the refrigerator.…”

“…Purification by Kugelrohr distillation gave aziridine 8 (730 mg, 88%) as a colourless oil, bp 60-80 ЊC/10 mmHg (lit., 23 60.5-61.5 ЊC/14 mmHg); data identical to those reported previously. 23 Aziridine 8 should be used immediately or stored under nitrogen in the refrigerator.…”

“…Prior to our work, aziridinocyclohexene oxides 1 were an unknown class of compound. However, since the corre- sponding aziridinocyclohexenes had been prepared previously 22, 23 and we had an ongoing interest in stereoselective epoxidation reactions, 24, 25 we elected to investigate an epoxidation route to meso-epoxides 1. By varying the nitrogen protecting group and the epoxidation conditions, we hoped to develop stereoselective syntheses of cis-and trans-diastereomeric epoxides 1.…”

“…The relative stereochemistry of all the epoxides described in this paper was established as outlined in Scheme 4. Thus, known 23 azido alcohol 17 (prepared by reaction of the monoepoxide of cyclohexa-1,4-diene 36 with sodium azide) was subjected to a molybdenum-catalysed, hydroxy-directed epoxidation reaction 37,38 to generate epoxide 18 in 96% yield. Epoxide 18 was obtained as the sole diastereomeric product and as a result of the hydroxy direction, the azido group and the epoxy group are trans relative to each other.…”

“…The combined aqueous layers were extracted with CH 2 Cl 2 (2 × 20 cm 3 ) and the combined organic extracts were dried (MgSO 4 ) and evaporated under reduced pressure to give the crude product. Purification by flash column chromatography on silica with petrol-EtOAc (1 : 1) as eluent gave N-tosylaziridine 10 (1.32 g, 78%) as a white crystalline solid, mp 111-113 ЊC (from 1 : 1 petrol-EtOAc)(lit., 23…”