BINOL based chiral phosphate

In 2009, Xiao employed a half sandwich Cp lr(l 11) complex with different chiral monosulfonated OPEN ligands (Figure 7.2), earlier developed for imine reduction by the same group, in combination with a BINOL based chiral phosphate counteranion (TRIP anion), to reductively aminate 24 acetophenone derivatives (1.2 equiv) with p anisidine (limiting reagent) under the conditions of 1.0 mol% of the indicated Ir catalyst (Table 7.1), 5 bar (73 psi) H2, toluene, 35 °C, and 15 24h [14]. 

Based on acid-base combination chemistry, Ishihara developed a catalytic enantioselective cyanosilylation of ketones by using chiral (J )-Ph2-BINOL-derived lithium phosphate, which was prepared in situ from phosphoric acid... 

Direct diastereo- and enantioselective hydrohydroxyalkylations of butadiene, an abundant petrochemical feedstock, required the use of a mthenium catalyst modified by a chiral phosphate counterion derived from Hg-BINOL. The anion is attached to the metal center through the acid-base reaction of H2Ru(CO)(PPh3)3 with the indicated chiral phosphoric acid. With the chiral counterion as the sole chiral inducing element, primary benzylic alcohols hydrohydroxyalkylate butadiene with good levels of anri-diastereo- and enantioselectivity (Scheme 3) [37]. 

The absolute configuration of the amine 7 may be explained by a stereochemical model based on the X-ray crystal structure of the chiral BINOL-phosphate (Fig. 4). In the transition state the ketimine is activated by the Brpnsted acid in such a way, that the nucleophile has to approach from the less hindered si face as the re face is effectively shielded by the large aryl substituent of the catalyst (Fig. 4, left). Furthermore, a bifunctional activation seems to be plausible, where next to the ketimine protonation, the dihydropyridine is activated through a hydrogen bond from the Lewis basic oxygen of the phosphoryl group. 

It is interesting that the condensation between electron-rich phenol, amine, and a chiral a -A, A -dibenzylamino aldehyde has been reported to be temperature sensitive, with high syn selectivity at high reaction temperatures while high anti selectivity is observed at low reaction temperatures. Similar to the Aldol Condensation, the Mannich reaction can be promoted or catalyzed by either acid or base. Furthermore, different protic acids or Lewis acid alone or in combination with a different chiral ligand or auxiliary group is used to enhance the stereoselectivity of the Mannich reaction, such as proline, (,S )-amino sulfonamide, BINOL phosphate," At-spiro chiral quaternary ammonium bromide, and dodecylbenzenesulfonic acid" as well as Lewis acids, such as Cu(OAc)2, CuC104, " Cu(OTf)2-chiral diamine complexes,... 

A novel class of chiral anions E based on a C2-symmetric imidodiphosphate anion was consequently designed featuring a single type of Brpnsted basic site as found in C2-symmetric phosphates A and B and increased steric bulk introduced via A-substitution like in anions C and D (Scheme 24). The catalyst architecture restricts the imidodiphosphate moiety to a single 0,0-syn conformation between two identical interlocking BINOL subunits with bulky 3,3 -substituents. In this way, rotation around P-N bonds is prevented giving geometrically fixed acid/ base pair. Additionally, the access to the undesirable alternative Brpnsted basic A-site is blocked. 

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