Science of Synthesis

van Leeuwen, P. W. N. M., Science of Synthesis: Stereoselective Synthesis, (2011) 1, 427.

Only since 1992–3 have useful rhodium catalysts for the asymmetric hydroformylation of vinyl aromatics become available, as until then the use of the diphosphines that were successful in asymmetric hydrogenation failed to give good enantioselectivity in rhodium-catalyzed asymmetric hydroformylation. Before that, platinum catalysts were used, which need high temperatures and pressures, and give large proportions of side products and considerable ligand (chiral diphosphines) decomposition.[‌86‌,‌87‌] More than a decade later, new phosphines were developed that would equal the discoveries of 1992 (see Section ‌1.9.1.6‌). In 1992 Takaya and Nozaki reported BINAPHOS (‌29‌, Ar1 = Ph), which turned out to be a multipurpose ligand for asymmetric hydroformylation and other carbonylation reactions.[‌22‌,‌88‌] In 1992 a patent from Union Carbide was published that showed the successful use of chiral diphosphites for asymmetric hydroformylation (see Section ‌1.9.1.8‌). In this section are presented the results of electronic variants of BINAPHOS and their effect on various substrates in asymmetric hydroformylation reactions (‌Scheme 13‌).[‌89‌] From the scheme it can be seen that ligand ‌29‌ (Ar1 = 3-MeOC6H4) containing a methoxy substituent in the 3-position gives for all three substrates a higher yield of the desired chiral, branched aldehyde.

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References