Hydroboration of olefin

Hydrogenation of olefins, enols, or enamines with chiral tVilkinson type catalysts, e.g., Noyort hydrogenation. Hydroboration of olefins with chiral boranes. Sharpless epoxi-dation of allylic alcohols. 

Catalytic Asymmetric Hydroboration. The hydroboration of olefins with catecholborane (an achiral hydroborating agent) is cataly2ed by cationic rhodium complexes with enantiomericaHy pure phosphines, eg, [Rh(cod)2]BE4BINAP, where cod is 1,5-cyclooctadiene and BINAP is... 

HYDROBORATION OF OLEFINS (+)-ISOPINOCAMPHEOL, 52, 59 Hydroboration-oxidation of olefins, 53, 83... 

Hydroboration of olefins catalyzed by the Wilkinson catalyst Rh(PPh3)3Cl has been the most studied reaction by quantum chemical calculations [25-27], In the following, three representative studies are described. 

HYDROBORATION OF OLEFINS CATALYZED BY EARLY TRANSITION METAL COMPLEXES... 

In this chapter, theoretical studies on various transition metal catalyzed boration reactions have been summarized. The hydroboration of olefins catalyzed by the Wilkinson catalyst was studied most. The oxidative addition of borane to the Rh metal center is commonly believed to be the first step followed by the coordination of olefin. The extensive calculations on the experimentally proposed associative and dissociative reaction pathways do not yield a definitive conclusion on which pathway is preferred. Clearly, the reaction mechanism is a complicated one. It is believed that the properties of the substrate and the nature of ligands in the catalyst together with temperature and solvent affect the reaction pathways significantly. Early transition metal catalyzed hydroboration is believed to involve a G-bond metathesis process because of the difficulty in having an oxidative addition reaction due to less available metal d electrons. 

The hydroboration of olefins at about room temperature leads to trialkylboranes by anti-Markownikoff addition 20) ... 

Boronic esters have been used in a wide range of transformations. These useful reagents have been transformed into numerous functional groups and are essential reagents for several C-C bond-forming reactions. Transition metal-catalyzed hydroboration of olefins often leads to mixtures of branched and linear products. Several groups have reported asymmetric reductions of vinyl boronic esters [50-52] with chiral rhodium P,P complexes however, the first iridium-catalyzed reduction was reported by Paptchikhine et al (Scheme 10) [53]. 

The hydroboration amination sequence in diglyme is a general procedure for the conversion of olefins to primary amines without rearrangement and with predictable stereochemistry.5 An alternative procedure, using tetrahydrofuran as solvent and either hydroxylamine-O-sulfonic acid or chloramine, is applicable with terminal olefins and relatively unhindered internal and alicyclic olefins.6 O-Mesitylenesulfonylhydroxylamine also gave desired amines in comparable yield.7 Alternative procedures for the hydroboration of olefins use commercially available solutions of di-borane in tetrahydrofuran8 or dimethylsulfide.9... 

Catalytic hydroboration of olefins with catecholborane (143) in the presence of Wilkinson catalyst was first reported in 1985 [78,79,80]. Although the reaction takes place without the catalyst, it requires high temperature. The Rh-catalyzed reaction proceeds smoothly at room... 

TABLE 2.5. Asymmetric Hydroboration of Olefins with Rhodium Catalysts and Catecholborane ... 

The hydrides 44b have been found to polymerize ethylene and react with a variety of protic reagents such as terminal alkynes and nitriles. Catalytic effects in the hydroboration of olefins have also been observed [27]. A well-defined /i-ethynyl complex of yttrium is formed by protolysis of the alkyl derivative 38b with acetylene (Eq. 18). Figure 14 shows the dimeric structure of 45b with bridging ethynyl ligands [27, 65]. 

Even an organolanthanide-catalyzed variant of the (anti-Markownikofl) hydroboration of olefins has been developed. The catalytic cycle is illustrated in Scheme 8. 

M. Zaidlewicz, Formation of C-0 Bonds by Hydroboration of Olefinic Double Bonds Followed by Oxidation, in Stereoselective Synthesis (Houben-Weyl) 4th ed. 1996, (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann, Eds.), 1996, Vol. E 21 (Workbench Edition), 8, 4519 1530, Georg Thieme Verlag, Stuttgart. 

Inspired by the chiral phosphine/oxazoline ligands developed by Helmchen and Pfaltz [131], Crudden and coworkers, have prepared a chiral NHC-oxazoline possessing a rigid backbone (Fig. 14) [ 132 ]. The rhodium complex 74 has been used in the catalytic hydroboration of olefins and the hydrosilylation of prochiral ketones with enantiomeric excesses that did not exceed 10%. 

Hydroboration of olefins has become very important in organic chemistry, mainly because of a secondary reaction, which is almost always carried out after it. In this re-... 

Why was it not possible to obtain alcohol 9 directly by hydroboration of olefin 7 ... 

---