BINAP

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In organic chemistry, BINAP, an acronym used for 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, is an important chiral ligand widely used in asymmetric synthesis. It consists of two naphthyl groups linked by a single bond with diphenylphosphino groups at the end of each naphthyl group (Figure 1). This framework is chiral, yet it has no stereogenic center (see axial chirality ). Rotation about the single bond binding the two naphthyl groups is restricted due to steric hindrance of the phosphine groups. Therefore the angle made by the two π planes is fixed to approximately 90˚ and two separate enantiomers exist, as shown in the figure:

This chiral structure of BINAP enables highly enantioselective reactions in organic synthesis. Enantioselective organic reactions catalyzed by BINAP complexes using transition metals such as ruthenium, rhodium, and palladium have been reported, with asymmetric hydrogenation catalyzed by Rh- and Ru-BINAP being pioneered by Ryoji Noyori, winner of the 2001 Nobel Prize in Chemistry, and his co-workers. The most important and well-known work in their studies is asymmetric synthesis of (-)-menthol, which is extensively used as a flavoring ingredient, catalyzed by Rh-BINAP. This synthetic method was industrialized by Takasago International Corporation, which provides (-)-menthol to pharmaceutical and food companies worldwide.

BINAP is prepared from BINOL (1,1'-bi-2-naphthol) via its bis-triflate derivatives. Both the R and S enantiomers as well as the racemate are commercially available.

References

1. ^  "Binap: An industrial approach to manufacture".
2. BINAP synthesis in Organic Syntheses, Coll. Vol. 10, p.112 (2004); Vol. 76, p.6 (1999) Article.
3. Asymmetric hydrogenation of methyl 3-oxobutanoate to (R)-Methyl 3-hydroxybutanoate with a ruthenium BINAP catalyst in Organic Syntheses, Coll. Vol. 9, p.589 (1998); Vol. 71, p.1 (1993) Article.