Enhancing the dienic reactivity of phospholes: an improved access to trivalent 7-phosphanorbornenes.
A structural comparison of 1-cyano- and 1-alkoxy-3,4-dimethylphospholes with 1-benzylphosphole has led to some unexpected conclusions. There is no univocal relationship between phosphole aromaticity and pyramidality at phosphorus. It has been found that both the highly pyramidal 1-cyanophosphole 1 (sigma(CPC angles) = 290 degrees), and the much less pyramidal 1-alkoxyphosphole 6 (sigma(CPC angles) = 310 degrees) have a low Bird aromaticity index (27 for both molecules), when compared to 1-benzylphosphole (sigma(CPC angles) = 303 degrees, BI = 35.5). This low aromaticity is correlated with a high reactivity of the diene in both 1 and 7 (similar to 6) toward acrylonitrile. Good stereochemical control is observed with 7, which gives exclusively the anti,endo [4 + 2] cycloadducts with acrylonitrile and diethyl vinylphosphonate.
Mattmann
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Laboratoire Hétéroéléments et Coordination UMR CNRS 7653, DCPH, Ecole Polytechnique, 91128 Palaiseau, France.
Simonutti
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D
Ricard
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L
Mercier
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F
Mathey
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F