Substituted 1,3-Butadienes and Non-conjugated Polyenes

As with 1,3-butadiene, also other conjugated dienes such as 1,3-pentadiene, iso-prene, or 1,3-cyclohexadiene also predominantly form monoaldehydes under the conditions of Rh catalysis [78]. 

As illustrated by the example of dicyclopentadiene, non-conjugated double bonds can be hydroformylated like isolated olefins, but rapid conjugation prior to the hydroformylation may prevent the formation of the expected poly-aldehydes. In the hydroformylation of 1,5-cyclooctadiene with unmodified Co or Rh catalysts, the main product was formyl cyclooctane [88]. In contrast, cycloheptatriene was formylated twice. The amount of triformylcycloheptanes did not exceed 10%. 

Hydroformylation of allenes (1,2-butadienes) was mentioned only once in the literature. Fell and Beutler [91] reacted allenes with syngas in the presence of HRh(CO)(PPh3)3 but obtained only a mixture of mono- and dialdehydes. In 2008, Guo and Ma [92] used 1,2-allenyl phosphine oxides and phosphonates as substrates and, under the control of the same catalyst, achieved exclusively the production of the terminal aldehydes. 

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