New ways of genterating organotion reactive intermediates for organic synthesis

Abstract

Progress in generating and applying two important organotin reactive species for organic synthesis is reported. - Stannyl radicals R 3Sn ., at present the most used tools for free radical synthesis of complicated target molecules, are generally obtained from the hydrides R 3SnH. In a number of cases, however, this is a drawback because of the high radical scavenging power of the latter. New ways of generating R 3Sn ., decoupling them from the presence of R 3SnH, are developed and discussed: the spontaneous thermal dissociation of distannanes with bulky substituents, the thermal fragmentation of bisstannyl benzpinacols, the ketone sensitized mild photolysis of simple distannanes, and the mild photolysis of benzyltin compounds such as 9-stannyl-9,10-dihydro anthracene. Examples of advantageous applications, also in combination with adjusted H donors, are given. - Stannyl cations R 3Sn + are used as superior leaving groups in electrophilic aromatic ipso substitution. Examples for their application under very mild conditions include the considerable broadening of the scope of the Friedel-Crafts acylation, the Vilsmeier formylation, sulfinations, and sulfonations. The directing influence of certain other substituents can be overcome by this ipso substitution.