Hydrometallation defined

The hydrometallation of alkynes is one of the most widely used routes to vinyl organometallics,131 which in turn are valuable in the construction of molecular structures containing carbon-carbon double bonds of defined stereochemistry. 

Generation of stereo- and regio-defined alkenylmetals via hydrometallation or carbometallation of alkynes followed by cross-coupling (Scheme 1-11) is a synthetically attractive notion for preparing arylated alkenes, conjugated dienes, and conjugated enynes. Its feasibility was demonstrated in 1976 [14,15] in the prototypical examples shown in Schemes 1-4 and 1-5. In these processes, hydroalumination was employed for generating the required alkenylmetals. 

For successful application of this strategy, ready access to vinyl halides with defined configuration of the carbon-carbon double bond is required. Such building blocks can be obtained via carbometallation of terminal alkynes [26] or by hydrometallation of internal alkynes, often with appropriate re-gioselectivity [27] (Scheme 3.16). 

Brown s discovery of the hydroboration reaction in the 1950s opened new avenues for the selective functionalization of olefins. The recognition that acyclic olefins can have well-defined conformational biases allowed the development of diastereoselective, substrate-controlled processes and the advent of the principles of acyclic stereocontrol. Given the central role the hydroboration of olefins has played, it is hardly surprising that the earliest examples in this field involve such transformations. For the organic chemist, diastereoselective and enantioselective hydrometalation reactions have rapidly become an indispensable tool equally useful in simple olefin functionalizations and in the stereoselective construction of highly complex molecules. 

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