Alkanes, direct borylation

Direct borylation of hydrocarbons catalyzed by a transition metal complex has been extensively studied by several groups and has become an economical, efficient, elegant, and environmentally benign protocol for the synthesis of a variety of organoboron compounds. The Rh-, Ir-, Re-, and Pd-catalyzed C-/H borylation of alkanes, arenes, and benzylic positions... 

Recently, rhodium-catalyzed direct borylation of alkane with diboron was reported [50], where Cp Rh(ri -CgMeg) (Cp =C5Me5) was used as a catalyst. This reaction has drawn considerable interest because the C-H o-bond activation and the introduction of some functional group into alkane were achieved in one pot. The similar reaction (Eq. 8) was theoretically investigated with the DFT method [51] ... 

Another strategy that bears potential is the direct borylation of alkanes, alkenes, and-most importantly - arenes by transition metal-catalyzed CH activation [39],... 

In terms of atom-economy a very attractive strategy for accessing arylboronic acids is the direct boronylation of arenes through a transition metal promoted C-H functionalization. In addition to the catalyst, a suitable boron donor is required, and both diboronyl esters and dialkoxyboranes are very appropriate in this role. The concept of this type of direct borylation was first demonstrated on alkanes using photochemical... 

C-H borylation of alkanes was first demonstrated by Hartwig using photochemical activation of Cp RefCOjj (Scheme 2.3) [51]. With irradiation from a 450 W medium-pressure Hanovia mercury arc lamp, alkylboronates are obtained by direct borylation of alkanes with pin2B2 in the presence of Cp Re(CO)j (2.4-5.0 mol%) and CO (2 atm). Pinacolborane is not effective for the borylation thus, one of two boron atoms participated in the catalytic cyde. All reactions resulted in high regiospecifidty for the functionalization of terminal primary carbons. 

The recent developments on the metallation chemistry of oxazoles and benzoxazoles, isoxazoles and benzisoxazoles, pyrazoles and indazoles, thiazoles and benzo-thiazoles, and isothiazoles, benzo[c]isothiazoles, and benzoMisothiazoles have been reviewed. The two-decade history of catalytic carbon-carbon bond formation via direct borylation of alkane C-H bonds catalysed by transition metal complexes has been reported. The alkane functionalization via electrophilic activation has been underlined. " Recent advances of transition-metal-catalysed addition reactions of C-H bonds to polar C-X (X=N, O) multiple bonds have been highlighted and their mechanisms have been discussed. The development and applications of the transition metal-catalysed coupling reactions have been also reviewed. - ... 

Bis(pinacolato)diborane(4) selectively adds to terminal aikenes and cyclic aikenes having internal strain to provide bis(boryl)alkanes in 76-86% yields 85-89 in the presence of a catalytic amount of Pt(dba)2 at 50 °C67 (Scheme 16). It is interesting to mention that Pt(dba)2 directed 1,2-addition to certain conjugated dienes, whereas 1,4-addition through a 7i-allyl-platinum(II) intermediate is an energetically more favorable process. The 1,4-addition to penta-1,3-diene at 80 °C with Pt(PPh3)4 gives 90, but the same reaction with Pt(dba)2 selectively produced the 1,2-addition product 91 at room temperature (Scheme 16). 

Initial reports on the borylation of alkanes using isolated transition-metal-boryl complexes date back to 1995, when Hartwig showed that Cp Re(CO)2(Bpin)2 converts pentane to 1-borylpentane with high regioselectivity. " The catalytic C-H borylation of alkanes with Cp Re(CO)3 using photochemical activation was demonstrated soon thereafter (equation 25). Also, an efficient thermal process that involves the use of rhodium catalysts has since been developed (equation 26). It is interesting to note that this methodology is not restricted to small molecules, but has recently been exploited for the direct side-chain functionalization of polyolefins. ... 

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