Alkenes, internal, chemoselective hydroformylation

A typical feature of hydroformylation is the fact that both sides of the double bond are in principle reactive, so only ethene yields propanal as a single product. From propene, two isomers are formed linear or normal butanal and 2-methylpropanal (branched or iso product). With longer chain 1-alkenes, the isomerization of the double bond to the thermodynamically more favored internal positions is possible, yielding the respective branched aldehydes (Fig. 1). Frequently, terminal hydroformylation is targeted because of the better biodegradability of the products. Thus, not only stability, activity, and chemoselectivity of the catalysts are important. A key parameter is also the regioselectivity, expressed by the n/i ratio or the linearity n/(n+i). 

Bulky diphosphites not only express a high selectivity toward 1-alkenes [255] but also for less reactive internal [256] and functionalized alkenes. Recently DSM and Du Pont reported on a ligand (24) which has a high regio- and chemoselectivity for the hydroformylation of methyl 3-pentenoate [253]. The synthesis of monophenols containing bulky substituents (25) is described in patents from Mitsubishi [257]. High yields with 1-alkenes and l/b ratios up to 20 are reported. 

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