An improved synthesis of pyridoxine (vitamin B6) is reported. The key step involves the light-promoted [2+2+2] cyclization of 3,3-bissilyl-di-2-propynyl ethers and acetonitrile in the presence of [cpCo(cod)] (1 mol%) as a catalyst. Convenient oxidation and iodination procedures are elaborated to transfer 3-silylpyridines into corresponding 3-hydroxy- and 3-iodo-derivatives.
Cocyclization of bis(trimethylsilyl)- and bis(trimethylstannyl)di-2-propynyl ether with acetonitrile provides a synthetic entry into 1,3-dihydro-6-methyl-4,7-bis(trimethylsilyl)- and bis(trimethylstannyl)-furo[3,4-c]pyridines. Regioselective electrophilic substitution of the respective silyl or stannyl groups allows for a regiocontrolled construction of tetrasubstituted pyridines. This method has been
双(三甲基甲硅烷基)-和双(三甲基锡烷基)二-2-丙炔基醚与乙腈的共环化可合成1,3-二氢-6-甲基-4,7-双(三甲基甲硅烷基)-和双(三甲基锡烷基)-呋喃[3,4- c ]吡啶。各自的甲硅烷基或苯乙烯基的区域选择性亲电子取代允许区域控制的四取代吡啶的构建。该方法已应用于维生素B 6的全合成。