Transition‐Metal‐Catalyzed Regioselective Functionalization of Monophosphino‐o‐Carboranes

Abstract

Af acile approacht ot he synthesis of diaryl-and dialkyl-substituted monophosphino-o-carboranes by rhodium(I)-catalyzed phosphine-directed B 3,6 ÀHa ctivationh as been developed for the first time. Upon switching rhodium(I) to palladium(II), C-arylateda nd B 6 -halogenated prod-ucts were obtained by using tBuOLi and Li 2 CO 3 as base, respectively.T hese discoveries provide some simple and efficient approaches to the modification of monophosphino-ocarboranes. 2k:P repared according to the general procedure to afford 58 mg (44 %) of 2k as aw hite solid. 1 HNMR (400 MHz, CDCl 3 ): d = 7.42-7.51 (m, 6H;A r), 7.33-7.38 (m, 4H;A r), 7.21-7.24 (m, 4H;A r), 3.84 ppm (s, 1H; HC cage ); 13 CNMR (101 MHz, CDCl 3 ): d = 135.9 (s; Ar), 135.9 (d, J = 1.0 Hz;A r), 135.7 (d, J C-P = 11.1 Hz;A r), 135.4 (d, J C-P = 12.1 Hz;A r), 131.9 (d, J C-P = 16.2 Hz;A r), 131.4 (d, J C-P = 14.1 Hz;A r), 131.3 (s;A r), 131.0 (s;A r), 128.8 (d, J C-P = 9.1 Hz;A r), 128.3 (d, J C-P = 10.1 Hz;A r), 128.0 (s;A r), 73.8 (d, J C-P = 76.8 Hz; 9f:P repared according to the general procedure to afford 144 mg (46 %) of 9f as aw hite solid. 1 HNMR (400 MHz, CDCl 3 ): d = 7.75-

Rh‐Catalyzed Decarbonylative Cross‐Coupling between o‐Carboranes and Twisted Amides: A Regioselective, Additive‐Free, and Concise Late‐Stage Carboranylation

“…In most cases, aryl bromide or aryl iodide works as the aryl source. But different from C−H activation, the B−O or B−halide byproduct, which was observed in our previous work and recent work reported by Che, can be generated due to the stronger bond energy of B−O, B−Br, or B−I bonds [20b, 23, 24c] . In addition, the weakly reductive o ‐carborane is sensitive to strong oxidants, and deboranation may happen when bases exist in the reaction system.…”

“…These results suggested that the other C cage should be blocked by alkyl or aryl to guarantee good yield and B(4) selectivity [24b, 25] . Ackerman reported the amide directed construction of B(3)− or B(3,4)−Ar, [22] while Che realized the syntheses of B(3,6)−C coupling compounds by irremovable PAr 2 DG (Figure 1 C, right) [23] . In most cases, aryl bromide or aryl iodide works as the aryl source.…”

“…The organometallic B(3,6)ÀHa ctivation has been investigated by Hawthorne, [14] Herbhold, [15] Xie, [16] Jin [17] and our group. [18] In recent years, several B(3)ÀC coupling reactions withoutd irecting groups have been disclosed (Figure 1C,l eft), [19] whilethe limited substrate scope has impeded their further applications.S ince either B(3) or B(4) is adjacent to cage carbons and the carbon vertex itself can be easily decoratedc ompared with other boron vertices,X ie, [20] Duttwyler, [21] Ackermann [22] and Che [23] ando ur laboratory [24] installed DGs on cage carbon so that aseries BÀCcoupling products were generated. Among them, the carboxylic acid, imine, "transient" imine, bidentate amide DGs resulted in B(4)À or B(4,5)ÀCf ormation.…”

“…[24b, 25] Ackerman reported the amide directedc onstruction of B(3)À or B(3,4)ÀAr, [22] while Che realized the syntheses of B (3,6)ÀCc oupling compounds by irremovable PAr 2 DG (Figure 1C,r ight). [23] In most cases, aryl bromide or aryl iodide works as the aryl source. But different from CÀH activation,t he BÀOo rB Àhalide byproduct, which was ob-served in our previous work andr ecent work reported by Che, can be generated due to the stronger bond energy of BÀO, BÀBr,o rB ÀIb onds.…”

Phosphorus‐Directed C−H Borylation

“…In this case, however, the phosphorus directing group was not maintained in the product. Examples of methods that could afford late‐stage functionalization of organophosphorus moieties through C−H functionalization began to be introduced in 2011 [80–88] . These transformations have been detailed in two recent reviews [89–90] and highlight the pioneering work by Kuninobu and Takai, [91] Satoh and Miura, [92–95] Glorius, [96] Kim and Lee, [97–105] Moon, [106] Yang, [107–109] and Park and Chang [110–111] .…”