Radical cyclisation by the use of α,β-unsaturated phosphonate as a radical acceptor was applied to a synthesis of 7-phosphonomethylpyrrolo[1,2-c]oxazolidinones, synthetic intermediates on the route to phosphonic acid analogues of kainoids. The relative configuration at the 6;7;7a-positions was found to be highly controlled by steric effects due to the substituent at the 6-position. Thus, diethyl [(6S*,7R*,7aS*)-6-(2-methoxyphenyl)-3-oxoperhydropyrrolo[1,2-c][1,3]oxazol-7-yl}methyl]phosphonate 29a and diethyl [(6S*,7R*,7aS*)-3-oxo-6-phenylperhydropyrrolo[1,2-c][1,3]oxazol-7-yl}methyl]phosphonate 29b were prepared with high diastereoselectivity. When the substituent at the 6-position is a 1-naphthyl group, the diethyl [(6S*,7R*,7aS*)-6-(1-naphthyl)pyrroloxazol-7-yl}methyl]phosphonate 29c and its (6S*,7R*,7aR*)-isomer 30c were formed in the ratio 29câ¶30c â 2â¶1. The stereostructure of compound 29a was determined by X-ray crystallographic analysis. The 6-o-methoxyphenyl derivative 29a was converted into the corresponding phosphonic acid analogue 33.
利用α,β-不饱和
膦酸酯作为自由基受体的激进环化反应被应用于7-膦酰甲基
吡咯并[1,2-c]
噁唑啉酮的合成,这些是通往类藻肽
磷酸类似物的合成中间体。发现在6;7;7a位置的相对构型受到6位取代基的立体效应的高度控制。因此,
二乙基[(6S*,7R*,7aS*)-6-(2-
甲氧基苯基)-3-氧代全氢
吡咯并[1,2-c][1,3]
噁唑啉-7-基}甲基]
膦酸酯29a和
二乙基[(6S*,7R*,7aS*)-3-氧代-6-苯基全氢
吡咯并[1,2-c][1,3]
噁唑啉-7-基}甲基]
膦酸酯29b以高度的非对映选择性制备。当6位取代基为1-
萘基时,
二乙基[(6S*,7R*,7aS*)-6-(1-
萘基)
吡咯噁唑啉-7-基}甲基]
膦酸酯29c及其(6S*,7R*,7aR*)异构体30c以29c:30c≈2:1的比例形成。化合物29a的立体结构通过X射线晶体学分析确定。6-邻
甲氧基苯基衍
生物29a被转化为相应的
膦酸类似物33。