Synthesis of Stereodefined Borylated Dendralenes through Copper-Catalyzed Allylboration of Alkynes.

An efficient method to access diversely substituted borylated dendralenes from simple and readily available materials is reported. This method is based on a multicomponent copper-catalyzed allylboration of alkynes with diboron and a 1,4-dibromo-2-butene which provides bromo- and boron-substituted skipped dienes with a remarkable chemo-, stereo-, and regioselectivity. These products can be easily transformed into dendralenic organoboronates, which display an extremely versatile reactivity as demonstrated by novel selective transformations.