ABSTRACT
α-Olefins are the most abundant petrochemical feedstock beyond alkanes, yet their use in commodity chemical manufacture is largely focused on polymerization and hydroformylation. The development of byproduct-free catalytic C-C bond-forming reactions that convert olefins to value-added products remains an important objective. Here, we review catalytic intermolecular reductive couplings of unactivated and activated olefin-derived nucleophiles with carbonyl partners. These processes represent an alternative to the longstanding use of stoichiometric organometallic reagents in carbonyl addition.
ABSTRACT
Chiral iridium complexes modified by SEGPHOS catalyze the 2-propanol-mediated reductive coupling of branched allylic acetates 1a-1o with formaldehyde to form primary homoallylic alcohols 2a-2o with excellent control of regio- and enantioselectivity. These processes, which rely on enantiotopic π-facial discrimination of σ-allyliridium intermediates, represent the first examples of enantioselective formaldehyde C-C coupling beyond aldol addition.
Subject(s)
Acetates/chemistry , Allyl Compounds/chemistry , Formaldehyde/chemistry , Propanols/chemical synthesis , Catalysis , Iridium/chemistry , Methylation , Oxidation-Reduction , StereoisomerismABSTRACT
Iridium catalyzed primary alcohol oxidation triggers reductive C-O bond cleavage of isoprene oxide to form aldehyde-allyliridium pairs that combine to form products of tert-(hydroxy)-prenylation, a motif found in >2000 terpenoid natural products. Curtin-Hammett effects are exploited to enforce high levels of anti-diastereo- and enantioselectivity in the formation of an all-carbon quaternary center. The present redox-triggered carbonyl additions occur in the absence of stoichiometric byproducts, premetalated reagents, and discrete alcohol-to-aldehyde redox manipulations.
Subject(s)
Alcohols/chemistry , Epoxy Compounds/chemistry , Terpenes/chemical synthesis , Vinyl Compounds/chemistry , Catalysis , Iridium/chemistry , Molecular Structure , Oxidation-Reduction , Prenylation , Stereoisomerism , Terpenes/chemistryABSTRACT
Heteroaromatic secondary alcohols react with isoprene to form products of hydrohydroxyalkylation in the presence of ruthenium(0) catalysts generated from Ru3(CO)12 and tricyclohexylphosphine, enabling direct conversion of secondary to tertiary alcohols in the absence of premetalated reagents or stoichiometric byproducts. The putative oxaruthenacycle intermediate has been isolated and characterized, and reversible metallacycle formation has been demonstrated.
Subject(s)
Alcohols/chemistry , Butadienes/chemistry , Hemiterpenes/chemistry , Organometallic Compounds/chemistry , Pentanes/chemistry , Ruthenium/chemistry , Alcohols/chemical synthesis , Alkylation , Catalysis , Heterocyclic Compounds/chemistry , Hydrocarbons, Aromatic/chemistry , Molecular Structure , Organometallic Compounds/chemical synthesis , Organometallic Compounds/isolation & purificationABSTRACT
Boronate ureas operate as catalysts for the activation of nitrocyclopropane carboxylates in nucleophilic ring-opening reactions. A variety of amines were found to open the urea-activated nitrocyclopropane carboxylates, generating highly useful nitro ester building blocks in good yields. Standard manipulations allow access to a wide range of valuable compounds from the ring-opened products with direct applications in bioactive target synthesis.
