Gram-Scale Synthesis of Dibenzo[a,e]pentalenes from Trialkyl(phenylethynyl)silanes via Organosodium Intermediates

Previous gram-scale synthesis of 5,10-disilyldibenzo­[a,e]­pentalenes (5,10-disilylDBPs), which serve as precursors of 5,10-dihaloDBPs, was accomplished by the reduction of trialkyl­(phenylethynyl)­silanes with highly pyrophoric potassium metals. Here we report two types of potassium-free and scalable synthesis of 5,10-disilylDBPs: (1) reduction of trialkyl­(phenylethynyl)­silanes with sodium dispersion (SD), and (2) reduction of trialkyl­(phenylethynyl)­silanes with lithium in the presence of NaOtBu. Both reactions involve 1,4-disodio-1,3-butadienes with an s-trans conformation as the key intermediates.

此前，5,10-二硅基二苯并[a,e]戊搭烯（5,10-disilylDBPs，作为5,10-二卤代二苯并[a,e]戊搭烯的前驱体）的克级规模合成，是通过高自燃性金属钾还原三烷基（苯乙炔基）硅烷实现的。本文报道两种无钾且可规模化的5,10-二硅基二苯并[a,e]戊搭烯合成方法：（1）以钠砂（SD）还原三烷基（苯乙炔基）硅烷；（2）在叔丁醇钠（NaOtBu）存在下，以金属锂还原三烷基（苯乙炔基）硅烷。两类反应均以具有s-trans构象的1,4-二钠-1,3-丁二烯作为关键中间体。