Oxaphosphetanes characterization

The first characterization of an oxaphosphetane prepared by a typical Wittig reaction was reported by Maryanoff et al. (22a). Thus, reaction of butylidenetriphenylphosphorane with benzaldehyde at — 78°C (THF LiBr present) was monitored by NMR. The spectrum contained two singlets at - 61.4 and — 63.8 ppm that were attributed to the cis and trans oxaphosphetanes, respectively. When this experiment was repeated with C-labeled starting materials, the chemical shifts and coupling constants of C3 and C4 in both isomers could be determined cis 71.5 ppm ( Jc p = 85 Hz), SC, ... 

All components of a complete Wittig reaction sequence, i.e. the starting phosphine, the phosphonium salts, the phosphorane, the oxaphosphetane and the phosphine oxide (Scheme 68) have been characterized by NMR spectroscopy and the electronic properties of 2-furyl and 3-furyl substituents evaluated by quantum chemical calculations including computational NMR spectroscopy. ... 

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