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 functionalized alkene or alcohol is inserted into the open face of a dicarbollide ion. Boron-insertion products of both ortho- and meta-carborane are synthesized, such as closo-3-(3-bromopropyl)-1,2 dicarba-dodecaborane, 6a, and closo-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 functionalization of the brominated products, 6a and 6b, to their respective acetate derivatives, 7a and 7b. Then, these acetate derivatives can be reduced 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-dodecaboranyl)-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 degraded by tetrabutylammonium fluoride to form their nido- derivatives, 12 and 13. The X-ray crystal structure of 9 is also presented. (C) 1999 Elsevier Science Ltd. All rights reserved.