Nickel- and palladium-catalyzed cross-coupling reactions at the bridgeheadof bicyclo[1.1.1]pentane derivatives - A convenient access to liquid crystalline compounds containing bicyclo[1.1.1]pentane moieties

Radical addition reactions of organyl iodides 7a-s onto [1.1,1]propellane ( 2) followed by halogen-lithium exchange and transmetallation with zinc chlo ride, as well as additions of Grignard reagents to 2, have furnished a vari ety of 3-substituted bicyclo[1.1.1]pentyl-1-magnesium (14) and -zinc (19) d erivatives. The latter have been coupled with various alkenyl, aryl, and bi aryl halides and triflates under NiCl2 dppe, Pd(PPh3)(4), or PdCl2(dppf) ca talysis to give a number of 1,3-disubstituted bicyclo[1.1.1]pentyl derivati ves 17, 20, and 23, several of which exhibit Liquid crystalline properties, in moderate to very good yields. The coupling products 20ca, 23ab, 23ae, 2 3ff, and 23fg have been further transformed to yield bicyclo[1.1.1]pentyl d erivatives 32, 24ab, 24ae, 27ff, and 27fg, respectively, bearing alkynyl, c yano, and/or alkenyl groups.