Chiral-Anion-Dependent Inversion of Diastereo- and Enantioselectivity in Carbonyl Crotylation via Ruthenium-Catalyzed Butadiene Hydrohydroxyalkylation

Abstract

The ruthenium catalyst generated in situ from H2Ru(CO)(PPh3)3, (S)-SEGPHOS and a TADDOL-derived phosphoric acid promotes butadiene hydrohydroxyalkylation to form enantiomerically enriched products. Notably, the observed diastereo- and enantioselectivity is opposite of that observed using BINOL-derived phosphate counterions in combination with (S)-SEGPHOS, the same enantiomer of chiral ligand. Match-mismatch effects between chiral ligand and chiral TADDOL-phosphate counterion are described. For the first time, single crystal X-ray diffraction data is reported for a ruthenium complex modified by a chiral phosphate counterion.

Ruthenium-Catalyzed Transfer Hydrogenation for C–C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs

“…38 It is postulated that the s- cis -conformer of butadiene hydrometalates to form a ( Z )-σ-crotylruthenium intermediate. The relatively Lewis basic TADDOL-derived phosphate counterion preserves the kinetic selectivity of diene hydrometalation by attenuating the degree of coordinative unsaturation, decelerating isomerization to the ( E )-σ-crotylruthenium haptomer with respect to carbonyl addition.…”

Metal-catalyzed reductive coupling of olefin-derived nucleophiles: Reinventing carbonyl addition

“…Enantioselective variants of the ruthenium catalyzed reductive couplings have been developed (26-29). Whereas initial studies relied on the use of 2-silyl-substituted dienes to direct syn -diastereo and enantioselectivity (26), chiral phosphate counterions (28) enable access to either the anti - or syn - diastereomers with good control of enantioselectivity (27, 28, 30). The collective data are consistent with a catalytic mechanism wherein alcohol dehydrogenation triggers diene hydrometalation (Figure 5).…”

Reductive C–C coupling via hydrogenation and transfer hydrogenation: Departure from stoichiometric metals in carbonyl addition

“…Corresponding transfer hydrogenative processes for carbonyl crotylation are achieved through the direct coupling of primary alcohols with butadiene, an abundant petrochemical feedstock, in the absence of stoichiometric byproducts (Scheme 3). 40,41 …”