Catalysis, boryl

Further insight into the P-borylation reaction of a,P-enones (Scheme 2.32) showed that the reaction can be carried out in THF, and the catalyst generated in situ from CuCl (5 mol%), the imidazolium salt (5 mol%), and NaO Bu (10 mol%), to form the [Cu(O Bu) (NHC)] as the catalysis initiating species. In this case, stable boron enolate products are formed which need to be hydrolysed by methanol to the ketone products [114]. 

Under catalysis by a Pd complex with homochiral phosphine ligand 19, silaboration of terminal allenes with homochiral silylborane 18 shows high enantioface-selectivity by double asymmetric induction (Equation (25)).lls The resultant /3-borylated allylsilanes can be used for asymmetric carbonyl allylation. 

Borate, Boryl and Borole Compounds and their Role in Olefin Polymerisation Catalysis... 

A relatively unstudied area of acid catalyzed derivatization is in the formation of boryl and boronate esters of ascorbic acid. The reaction of ascorbic acid with triethylborane using organic acid catalysis affords the... 

C-H borylation is a widely used methodology for the synthesis of organoboronates [63-65]. Most of the applications have been presented for the synthesis of aryl-boronates. However, functionalization of alkenes has also attracted much interest [66, 67]. In most applications, iridium catalysis was used. However, in case of alkenes, borohydride forms as a side product of the C-H borylation, which undergoes hydroboration with alkenes. This side reaction can be avoided using palladium catalysis under oxidative conditions. In a practically useful implementation of this reaction, pincer-complex catalysis (Ig) was appHed (Figure 4.17) [51]. The reaction can be carried out under mild reaction conditions at room temperature using the neat aUcene 34 as solvent. In this reaction, hypervalent iodine 36, the TFA analog of 29, was employed. In the absence of 36, borylation reaction did not occur. 

C—H borylation of indoles has been reported by a number of groups. Chirik and coworkers utilized pincer-ligated cobalt complexes with N-methyhndole and recorded the C-2 borylated indole (133) as the major product (2014JAC4133). The catalysts employed demonstrated high catalysis turnover and low catalytic loading and also demonstrated efficacy with other electron-rich heteroarenes (furan, thiophene, benzofuran) as well as electron-deficient pyridines. More recendy, platinum-NHC complexes have been used in the selective C—H borylation of indoles (2015JAC12211). The authors reported higher isolated yields with this... 

Borylated pyrrole 88 was prepared by Oestreich by treatment of the corresponding pyrrole with pinacolborane and a ruthenium(II) thiolate complex. The direct synthesis of 88 promises to find wide utility in medicinal chemistry and was applied to a variety of substituted indoles (13JA10978). N-Methylpyrrole was directly arylated at room temperature by photoredox catalysis with diaryliodonium salts to furnish 89 in 84% yield (13SL507). 

Hydroboration of Pyridines. P)ridines could be hydroborated under Rh catalysis to furnish A-borylated 1,2-dihydropyridines. Maximal yields and the least amount of A-borylated 1,4-dihydropyridine could be obtained with PCy3 compared with other phosphines. Triphenylphosphine and PCys produced diminished yields and favored the 1,4-dihydropyridine product (eq 41). 

The same year, Gandon et al. reported the synthesis of fused arylboronic esters 36 via cobalt(0)-mediated cycloaddition of alkynylboronates 33 with diynes 35 (Scheme 1.11) [22], The boronate is first reacted with Co2(CO)g at room temperature for 4 h to generate the corresponding dicobaltatetrahedrane 34. The diyne is then added and the mixture is refluxed for 2 h. To show the utility of the products, one of them was treated with phenyl iodide under Pd catalysis to give 37. Complementary to these investigations, Ru-catalyzed [2 - - 2 - - 2] cycloaddition of tethered alkynyl-boronic esters with alkynes was reported [23]. In this case, the borylated arene could not be isolated but was converted directly in situ by Suzuki-Miyaura coupling. 

---