Alkenylbenzenes, hydroformylation

Only a few examples of alkenylbenzene hydroformylation are available. Styrene and a-methylstyrene were reported to lead to hydrogenation as the main reaction when Co2(CO)8 was used. 

Hydroformylation of Alkenylbenzenes. Allylbenzene, trans- and cw-Propenylbenzene. Hydroformylation of these three isomeric alkenylbenzenes leads to propylbenzene (17) and to these aldehydes (18, 19, 20) (6,7,8) ... 

E)-2-phenyl-2-butene. Hydroformylation of this alkenylbenzene leads to four aldehydes (two of them diastereoisomers) and to the following saturated hydrocarbons ... 

With Rh, the phenomena are strikingly different since the aromatic ring does not influence the selectivity which is always very high, no matter what olefinic structure (except for 1,1-diphenylpropene). Isomer selectivity depends on several factors, mainly the structure and the stereochemistry of the alkenylbenzene. With conjugated alkenylbenzenes, addition of the CHO group occurs preferentially on the a carbon when the a and / carbons are monosubstituted. When the ft carbon is disubsti-tuted, because of steric requirements, hydroformylation is less selective and occurs on both the a and y carbon ... 

---