The direct, by-product–free conversion of basic feedstocks to products of medicinal and agricultural relevance is a broad goal of chemical research. Butadiene is a product of petroleum cracking and is produced on an enormous scale (about 12 × 106 metric tons annually). Here, with the use of a ruthenium catalyst modified by a chiral phosphate counterion, we report the direct redox-triggered carbon-carbon coupling of alcohols and butadiene to form products of carbonyl crotylation with high levels of anti-diastereoselectivity and enantioselectivity in the absence of stoichiometric by-products.
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.
The ruthenium catalyst derived from Ru3(CO)12 and triphos [Ph2P(CH2CH2PPh2)2] promotes the direct C–C coupling of isoprene with aryl substituted hydantoins 1a–1f at the diene C4-position to furnish products of n-prenylation 2a–2f. A mechanism involving hydantoin dehydrogenation followed by diene-imine oxidative coupling to furnish a transient aza-ruthencyclopentene is proposed.
The direct approach: Ruthenium(0)‐catalyzed hydrohydroxyalkylation of α‐olefins and styrenes with 3‐hydroxy‐2‐oxindoles forms branched products of CC coupling with high levels of diastereocontrol. A mechanism involving diene–olefin oxidative coupling and a subsequent carboxylic acid co‐catalyzed transfer hydrogenolysis of the resulting oxaruthenacycle intermediate is postulated.
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