The free radical chemistry of carboxylic esters of 2-selenopyridine-N-oxide: a convenient synthesis of (L)-vinylglycine |
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Authors: | Derek HR Barton David Crich Yolande Hervé Pierre Potier Josiane Thierry |
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Institution: | Institut de Chimie des Substances Naturelles, C.N.R.S. 91190 Gif-sur-Yvette, France |
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Abstract: | Optically pure (L)-vinylglycine has been synthesised by two different methods. The first of these involves protected (L)-glutamate esters of -hydroxy-2-seleno-pyridine. Such esters are shown to undergo the same decarboxylotive rearrangement as their thio-analogues. Oxidative elimination of the selenopyridine residue with ozone, and with the aid of hex-1-ene as sacrificial olefin for the work-up, gave the desired (L)-vinylglycine derivatives. Similarly, the modified Hunsdiecker reaction on the terminal carboxyl of suitably protected (L)-glutamic derivatives gave the nor-bromide which readily afforded the corresponding phenylselenides on treatment with phenylselenide anion. The sequence was then as above. Using the methyl ester with corbobenzyloxy protection for the amino-function an overall yield of crystalline optically pure (L)-vinylglycine of about 45% was obtained by either route. |
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