Cycloadditionen von 6H-1,3,4-Oxadiazin-6-onen (4,5-Diaza-α-pyronen), 10. Reaktionen von Bicyclo[2.1.1] hexenen mit 6H-1,3,4-Oxadiazin-6-onen und dynamische Effekte in einem neungliedrigen, überbrückten, α,β-ungesättigten Enollacton2)

Abstract

Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 10 1). – Reactions of Bicyclo[2.1.1]hexenes with 6H-1,3,4-Oxadiazin-6-ones and Dynamic Effects in a Nine-Membered, Bridged, α,β-Unsaturated Enol Lactone 2) The reactions of bicyclo[2.1.1]hexene (2) and its tricyclic derivative 3 with 2,5-diphenyl-6H-1,3,4-oxadiazin-6-one (1 a) gave the 3,4-dihydro-α-pyrones 6 and 7, respectively. In contrast, the methyl phenyloxadiazinonecarboxylate 1 b and 2 afforded a mixture of the nine-membered, bridged, α,β-unsaturated enol lactone 11 and the β-lactone 12 in a ratio of about 10: 1. Olefin 3 reacted with 1 b to furnish small amounts of the bridged derivative 16 of 11 as well as the 2:1 product 14, a saturated δ-lactone. Unlike 16, enol lactone 11 reveals dynamic phenomena, which have been investigated by means of line shape analyses of the temperature dependent 13C-NMR spectra. The interconvertion of the cis- and trans-lactone conformers (11 a ⇄ 11 b), being present in a 1:2 ratio, proceeds with δH‡c,t = 48.8 kJ mol−1, whereas the racemization of the trans-lactone enantiomers (11 b 11 b´) requires less activation (δH‡t,t = 42.3 kJ mol−1). The structure of cis-lactone 11 a has been established by an X-ray analysis.