Synthesis Of Bis-o-carboranes And N-heterocyclic O-carboranes Via B-H Activation

The selective B-H functionalization methodology of o-carborane is the focus,difficulty and hotspot in the field of carborane chemistry.In the previous works,the coupling units with o-carboranes are mainly prefunctionalized substrates such as arylhalide or arylboronic acids.However,the direct B-H/X-H(X=B,C,N,et al)coupling which is more atom and step economy was rarely reported.In this dissertation,three pioneering researches on oxidative dehydrogenation coupling of B-H/X-H(X=B,C,N,et al)were carried out.1)A series of bis(o-carborane)s connected by B(4)-B(4)' and B(4)-B(5)' bonds was synthesized with moderate to good yields via palladium catalyzed oxidative dehydrogenative coupling of cage B-H/B-H bonds by amide directing for the first time.Which solved the problem that it was difficult to synthesize such bis(o-carborane)s connected by B-B bond in traditional methods.This work opens the door for miscellaneous applications of bis(o-carborane)in related disciplines and has important value in design and synthesis of different kinds of B-B'-biscarboranes.2)In order to expand the strategy of direct B-H/B-H oxidative dehydrogenative coupling,we chose 1-pyridyl-o-carborane as substrate and a series of bis(o-carborane)s connected by B(3)-B(3)' and B(3)-B(6)' bonds was synthesized with moderate to good yields via palladium catalyzed oxidative dehydrogenative coupling of cage B-H/B-H bonds by pyridyl directing.This work verified the generality of the direct B-H/B-H oxidative dehydrogenative coupling strategy for synthesis of bis(o-carborane)s,enriched the type of B-B' bis(o-carborane)s,and has important reference for design,synthesis,and application of bis(o-carborane)s in related fields.3)On the base of the previous two works,the strategy of B-H/B-H oxidative dehydrogenation coupling was extended to B-H/C-H and B-H/N-H oxidative dehydrogenation coupling.A series of carborano-isoquinolinone derivatives was synthesized with moderate to good yields by cascade oxidative dehydrogenation cross-coupling of B-H/C-H and B-H/N-H utilize the parent o-carboborane and benzoamides as substrates.This cascade transformation was carried out in two steps.Firstly,the parent o-carboborane and benzoamide are dehydrogenated cross-coupling under the catalysis of Ir(?)to obtain B(3)-arylamide products;the second dehydrogenation cross-coupling of B(7)-H with amide N-H under the catalysis of Pd(?).This method does not need prefunctionalization,has good step economy and atomic economy,which is very in line with the green chemical development concept advocated by the state,and provides a new reference for the direct B-H functionalization of the parent o-carboborane.4)On the base of the previous three works about B-H activation,we hope to realize more B-H/X-H dehydrogenation coupling reaction by directing groups assist.However,the premise of such research work is to have a methodology for preparation o-carborane substrates containing directing groups.A FeCl3 catalyzed tandem condensation/cyclization/aerobic oxidation process for synthesis of 1-benzoxazolyl-o-carboranes has been developed.The degradation of o-carborane in the presence of aza-/oxa-nucleophiles was completely suppressed,and a series of 1-benzoxazolyl-o-carboranes,1-benzothiazolyl-o-carborane and 1-benzimidazolyl-o-carborane have been synthesized with good to excellent yields.This work offers a general protocol for synthesis of 1-benzoxazolyl-o-carboranes,which has important reference for synthesis of aromatic heterocycle-carborane derivatives and promote its applications in miscellaneous areas.