Abstract
A small library of bisphosphorus ligands was evaluated in the rhodium‐catalyzed isomerizing hydroformylation (I‐HF) of cashew nut shell liquid (CNSL). The rhodium complex of 1,2‐bis((di‐tert‐butylphosphanyl)methyl)benzene (BDTBPMB; L4) outperformed the other bisphosphite and bisphosphine ligands and unveiled a moderate selectivity of 28 % and 50 % in the I‐HF of CNSL monoene and methoxy‐protected monoene, respectively. The resultant aldehyde 16‐(3‐methoxyphenyl)hexadecanal P1′ was isolated and its identity was fully established. Application of bis‐phosphine ligand L4 in the I‐HF of highly challenging CNSL cardanol (S3) and methoxy‐protected CNSL cardanol yielded a linear selectivity of 74 %, although with reduced conversion. To demonstrate the synthetic utility of our strategy, the obtained aldehyde (derived from S3) was subjected to hydrogenation and the resultant 3‐(16‐hydroxyhexadecyl) phenol (P8) was isolated in 89 % isolated yield. High‐pressure NMR investigation revealed selective formation of a bis‐equatorial BDTBPMB–rhodium complex, which might be responsible for the excellent linear selectivity.
What a nut! An in situ generated catalyst delivers a terminal selectivity of 74 % in the isomerizing hydroformylation of cashew nut shell liquid and the synthetic utility of this strategy has been demonstrated by converting the resultant aldehydes into unsymmetrical α,ω‐difunctional molecules.