Radical reactions leading to substituted pyroglutamates
作者:S. Richard Baker、Andrew F. Parsons、Michelle Wilson
DOI:10.1016/s0040-4039(98)00254-8
日期:1998.4
The Bu3SnH mediated cyclisation of a serine-derived dehydroalanine was shown to provide an efficient approach to a protected 4-phenylpyroglutamate which was elaborated to 4-phenylglutamic acid in good yield. Cyclisation reactions of this type were shown to proceed via an intermediate captodative radical which could be trapped intermolecularly using an alkene e.g. styrene or methyl methacrylate. This
Baker, S. Richard; Goodall, Karen; Parsons, Andrew F., Journal of Chemical Research, Miniprint, 2000, # 7, p. 837 - 852
作者:Baker, S. Richard、Goodall, Karen、Parsons, Andrew F.、Wilson, Michelle
DOI:——
日期:——
Is an Iodine Atom Almighty as a Leaving Group for Bu<sub>3</sub>SnH-Mediated Radical Cyclization? The Effect of a Halogen Atom on the 5-Endo-trig Radical Cyclization of <i>N</i>-Vinyl-α-halo Amides
The effect of a halogen atom as a leaving group on Bu3SnH-mediated 5-endo-trig radical cyclization of N-(cyclohex-l-enyl) alpha-halo amides was examined. The cyclization of alpha-chloro amides occurred with a high degree of efficiency, whereas the corresponding alpha-iodo congeners gave only limited quantities of cyclization products. A detailed study revealed that these phenomena could be attributed to the initial conformations of alpha-halo amides. The cyclizing ability of alpha-iodo amides can be restored with Bu3SnCl or Bu3SnF as an additive. The cyclization of an alpha-iodo amide in the presence of Bu3SnF could be applied to a short-step synthesis of lycoranes featuring sequential 5-endo-trig and 6-endo-trig radical cyclizations.