Regio- and Enantiocontrol in the Room-Temperature Hydroboration of Vinyl Arenes with Pinacol Borane

Abstract

The catalyzed hydroboration of vinyl arenes was carried out using pinacol borane instead of catechol borane, as the former reagent and the product boronates are significantly easier to handle. By careful choice of catalyst, either the branched or the linear product can be obtained in greater than 96% selectivity. Interestingly, common ligands such as BINAP and Josiphos give opposite asymmetric induction with pinacol borane as compared with catechol borane, while P,N-ligands such as Quinap gave the same sense of induction. The hydroboration of 6-methoxynaphthalene proceeded with the greatest regio- (95:5) and enantioselectivity (94:6) of all vinyl arenes examined. The hydroboration product was then employed in a concise synthesis of the nonsteroidal antiinflammatory agent, Naproxen.

Synthesis, Structure, and Catalytic Studies of Palladium and Platinum Bis-Sulfoxide Complexes

“…The catalytic version of this reaction has been most welldeveloped with rhodium catalysts. [47][48][49][50][51][52][53][54][55][56][57][58][59][60] There is very little in the current literature regarding the use of platinum in hydroboration reactions. There is only one example of catechol borane being used in the hydroboration of a terminal alkene with a platinum catalyst.…”

Reductive Cross‐Coupling of Conjugated Arylalkenes and Aryl Bromides with Hydrosilanes by Cooperative Palladium/Copper Catalysis

“…[6] Ther esulting 1-arylalkylmetal reagents are subsequently purified and used for the cross-coupling with aryl halides. Sigman and co-workers then developed reductive crosscoupling reactions of styrenes with arylstannanes [7a] or arylboronic esters [7b] in the presence of iPrOH as ahydrogen source to afford 1,1-diarylethanes via an alkylpalladium species [Eq.…”

The Development of Enantioselective Rhodium-Catalysed Hydroboration of Olefins

“…In general, 1,1-disubstituted alkenes gave a lower yield of anti-Markovnikov alcohol after oxidation ( < 30%), entries 1 and 5, than did internal alkenes: 58 -93% of Markovnikov product, entries 6 -9, comparing results obtained with (S,S)-DIOP (24). All chiral diphosphine ligands employed were effective, irrespective of the type of chirality present, entries 1 -4.…”

“…[11,87] "Asymmetric amplification" experiments provided no evidence to suggest there was more than one phosphine ligand per catalyst molecule but did not conclusively rule out that possibility either. [94] Subsequently, Burgess [95] prepared a series of hybrid ligands 51 -53, Figure 5, which were chiral not only in the carbon backbone like (R,R)-DIOP (24), but also at phosphorus, like DIPAMP (50).…”

“…Among recent examples that highlight the synthetic utility of this methodology are its direction towards a formal synthesis of the non-steroidal anti-inflammatory agents Ibuprofen TM and Naproxen TM , [13,14,24] as well as the anti-depressant Sertraline. [25] Attempts to expand the range of substrates to include cyclopropenes [19] and norbornene-derived meso-bicyclic hydrazines [26] have recently been reported.…”