Synthesis and characterization of ortho-3-and meta-2-substituted carboranes through a boron-insertion reaction, including the structure of the product of a double-insertion reaction

Examples of boron-insertion reactions are presented in which either a funct ionalized alkene or alcohol is inserted into the open face of a dicarbollid e ion. Boron-insertion products of both ortho- and meta-carborane are synth esized, such as closo-3-(3-bromopropyl)-1,2 dicarba-dodecaborane, 6a, and c loso-2-(3-bromopropyl)-1,7-dicarbadodecaborane, 6b. While the ortho-3- and meta-2-alkylhydroxycarborane derivatives, 8a or 8b, respectively, cannot be synthesized directly using this method, they can be prepared first by func tionalization of the brominated products, 6a and 6b, to their respective ac etate derivatives, 7a and 7b. Then, these acetate derivatives can be reduce d to the alcohols, 8a and 8b, respectively. Symmetric or asymmetric double boron-insertion reactions were employed for synthesis of 1,6-bis(closo-1,2- dicarba-3-dodecaboranyl) hexane, 9, and 1,4-bis(closo-1,2-dicarba-3-dodecab oranyl)-1-oxabutane, 11. Both types of boron-insertion products, 4-(closo-1 ,2-dicarba-3-dodecaboranyl)-4-oxabut-1-ene, 10, and 8a can be selectively d egraded by tetrabutylammonium fluoride to form their nido- derivatives, 12 and 13. The X-ray crystal structure of 9 is also presented. (C) 1999 Elsevi er Science Ltd. All rights reserved.