Olefins regiocontrol

Scheme 28 Examples of two aspirational processes byproduct-free couplings of a-olefins to (renewable) alcohols and amines with linear or branch regiocontrol...

On the other hand, the cationic complex [lr(cod)(PR3)2] [PF6] appeared a very good catalyst for migration of the C=C bond to be applied for the regiocontrolled synthesis of allylsilane from olefin silylation at a remote sp carbon (Scheme 14.13) [82]. 

Asymmetric olefins, which carry more alkyl substituents at the Ce center than at the Ca center, are also hydroborated by the unhindered BH3 with considerable regioselectivity (Table 3.1). After oxidative workup, one isolates the alcohol in the a position almost exclusively. According to what has already been stated, as the more bulky reagent, 9-BBN reacts with more sensitivity to steric effects than BH3 and its secondary products. It therefore makes possible olefin hydrations with almost perfect regiocontrol. 

If one wants to obtain olefins by an H/Het elimination from R—Het, there are evidently unpleasant limitations with respect to regiocontrol (Section 4.1.4) and stereocontrol (Section 4.1.3). Most of these limitations disappear when the same olefin is synthesized by a /3-elimination of HetVHet2 ... 

REGIOCONTROLLED HECK ARYLATION OF ELECTRON-RICH OLEFINS... 

In addition to enantiocontrol, the problem of regiocontrol arises in these reactions. There are various factors that influence the regioselectivity of allylic substitutions [3,4,13, 36, 37, 38, 39]. Electronic effects exerted by the catalyst and the allylic substituents, steric interactions between the nucleophile, the allyl system and the catalyst, and the relative stabilities of the Ti-olefin complexes formed after nucleophilic addition, can all play a role. The relative importance of these factors varies with the catalyst, the substrate, the nucleophile, the solvent and other reaction parameters and is difficult to predict. 

M 10. Krafft, M.E. Regiocontrol in the Intermolecular Cobalt-Catalyzed Olefin-Acetylene Cycloaddition J. Am. Chem. Soc. 1988,110, 968-970... 

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