Cooperative Catalysis: Enantioselective Propargylic Alkylation of Propargylic Alcohols with Enecarbamates Using Ruthenium/Phosphoramide Hybrid Catalysts

Abstract

The diastereo-and enantioselective propargylic alkylation of propargylic alcohols with E-enecarbamates in the presence of a catalytic amount of thiolate-bridged diruthenium complexes bearing an optically active phosphoramide moiety gives the corresponding propargylic alkylated products (up to 97 % ee).

Recent Developments in Enantioselective Transition Metal Catalysis Featuring Attractive Noncovalent Interactions between Ligand and Substrate

“…In 2015 Nishibayashi and co-workers reported the diastereo- and enantioselective alkylation of propargylic alcohols with enecarbamates ( Figure 35 a). 131 The authors designed a novel hybrid catalyst which contained a thiolate-bridged diruthenium complex linked to a phosphoramide based on ( R )-BINOL ( Figure 35 b). It was hypothesized that the phosphoramide could activate enecarbamates through hydrogen bonding and also control the facial selectivity of nucleophilic attack onto a ruthenium-allenylidene intermediate.…”

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

“…A recent example reported by the Li group describes an application of the process to coumarine synthesis (Scheme 93). The reaction of phenylacetylene (305) and salicylaldehyde (450) in the presence of Wilkinson's catalyst and 4-picoline N-oxide afforded coumarine 451 in excellent yield through a tandem sequence involving ketene generation, phenol addition, and intramolecular aldol condensation. 265 The metalloketene intermediate was shown to be capable of participating in electrocyclization (Scheme 94).…”

“…Using the dinuclear ruthenium catalyst, having a chiral phosphoramide attached to its bridged thiolate ligands, the reaction of otolyl propargyl alcohol 941 with enamide 942 took place with high enantio-and diastereoselectivity, furnishing alkynone 943 after hydrolytic workup (Scheme 189). 450 It is proposed that the hybrid catalyst, capable of hydrogen bonding with the nucleophile, renders the π-facial stereodiscrimination more pronounced. The bifunctional hybrid catalyst proved superior to a dual-catalytic system employing achiral [Cp*Ru(μ 2 -SMe)Cl] 2 in combination with a chiral phosphoramide, which gave 943 with an ee of only 4%.…”

Mechanistic Insights into the Appel Reaction Mediated by a Poly-Phosphamide Material as a Heterogeneous Catalyst

“…20 Moreover, the phosphamide has also been used as a ligand to stabilize the ruthenium complex, which can perform enantioselective propargylic alkylation on the propargylic alcohols. 21 Apart from their catalytic activity, phosphamides show immense thermal stability, and the phosphamides supported on SiO used as flame retardants (Scheme 1b). 22 Phosphoramideembedded polymers with porous structures have been shown to behave as adsorbents of phenol from wastewater.…”

“…Lately, phosphamides are also used as mediators to catalyze diverse organic reactions such as cross Aldol, Michael addition, borane reduction of ketones, preparation of nitro olefin, N -allylic alkylation, C–H activation, indolyl aromatic ring preparation, and Friedel–Crafts alkylation (Scheme a) . Moreover, the phosphamide has also been used as a ligand to stabilize the ruthenium complex, which can perform enantioselective propargylic alkylation on the propargylic alcohols . Apart from their catalytic activity, phosphamides show immense thermal stability, and the phosphamides supported on SiO 2 are widely used as flame retardants (Scheme b) .…”