Highly efficient Barbier allylation from allyl alcohol using iridium(I)/tin(II): Unusual and indirect roles of allyl alcohol and tin

Copper(I)-Catalyzed Asymmetric Nucleophilic Addition to Aldehydes with Skipped Enynes

The development of sustainable and novel strategies for constructing complex chiral molecules with versatile transformation potential is a long-term pursuit in the chemistry community. We report a copper(I)-catalyzed enyne addition to aldehydes under proton-transfer conditions, unlike previous examples which were limited to the use of preformed reactive nucleophiles containing allylic heteroatoms or electron-withdrawing groups. This protocol provides an efficient platform for installing chiral allylic alcohol moieties with a broad substrate scope and high regio-, stereo-, and enantioselectivity.

Transition metal catalysis—a unique road map in the stereoselective synthesis of 1,3-polyols

The present review summarizes recent diverse reactions employed in the formation of 1,3-polyols providing an overview of the mechanistic pathway and the enantioselectivity obtained, in terms of the properties of transition metals directly involved in the catalytic transformations and their interaction with various ligands.

Ni-catalyzed asymmetric reductive allylation of aldehydes with allylic carbonates

Asymmetric umpolung allylation of aldehydes with allylic carbonates was achieved for the first time using Ni-catalyzed reductive conditions.

Formation of C-C Bonds via Iridium-Catalyzed Hydrogenation and Transfer Hydrogenation

The formation of C-C bonds via catalytic hydrogenation and transfer hydrogenation enables carbonyl and imine addition in the absence of stoichiometric organometallic reagents. In this review, iridium-catalyzed C-C bond-forming hydrogenations and transfer hydrogenations are surveyed. These processes encompass selective, atom-economic methods for the vinylation and allylation of carbonyl compounds and imines. Notably, under transfer hydrogenation conditions, alcohol dehydrogenation drives reductive generation of organoiridium nucleophiles, enabling carbonyl addition from the aldehyde or alcohol oxidation level. In the latter case, hydrogen exchange between alcohols and π-unsaturated reactants generates electrophile-nucleophile pairs en route to products of hydro-hydroxyalkylation, representing a direct method for the functionalization of carbinol C-H bonds.

Synthesis of cinnamyl ethers from α-vinylbenzyl alcohol using iodine as catalyst

Reactions of α-vinylbenzyl alcohol with other alcohols using iodine as a catalyst were investigated. The corresponding cinnamyl ethers were obtained as products. This suggested that α-vinylbenzyl alcohol was converted to cinnamyl ethers via 1-phenylallyl cation. Cinnamyl ethyl ether was obtained in 75% yield by the reaction of α-vinylbenzyl alcohol and ethanol in acetonitrile with iodine under the following conditions: temperature = 50 °C, molar ratio of α-vinylbenzyl alcohol:ethanol:iodine = 1:3.0:0.2, and time period = 6 h. Generally, the yields of the reactions using primary alcohols were higher than those using secondary and tertiary alcohols. Ether interchange also occurred by the reaction of α-vinylbenzyl alcohol and iodine, but proceeded smoothly only when an allyl group was used as the other substituent of the starting ether.

Enantioselective iridium-catalyzed carbonyl allylation from the alcohol oxidation level via transfer hydrogenation: minimizing pre-activation for synthetic efficiency

Existing methods for enantioselective carbonyl allylation, crotylation and tert-prenylation require stoichiometric generation of pre-metallated nucleophiles, and often employ stoichiometric chiral modifiers. Under the conditions of transfer hydrogenation employing an ortho-cyclometallated iridium C,O-benzoate catalyst, enantioselective carbonyl allylations, crotylations and tert-prenylations are achieved in the absence of stoichiometric metallic reagents or stoichiometric chiral modifiers. Moreover, under transfer hydrogenation conditions, primary alcohols function dually as hydrogen donors and aldehyde precursors, enabling enantioselective carbonyl addition directly from the alcohol oxidation level.

1,n-glycols as dialdehyde equivalents in iridium-catalyzed enantioselective carbonyl allylation and iterative two-directional assembly of 1,3-polyols

Unstable? We're able! 1,n-Glycols serve as synthetic equivalents to unstable dialdehydes in two-directional carbonyl allylation from the alcohol oxidation level under iridium-catalyzed transfer hydrogenation conditions. Iterative asymmetric allylation employing 1,3-propanediol enables the rapid assembly of protected 1,3-polyol substructures with exceptional levels of stereocontrol.

anti-Diastereo- and enantioselective carbonyl crotylation from the alcohol or aldehyde oxidation level employing a cyclometallated iridium catalyst: alpha-methyl allyl acetate as a surrogate to preformed crotylmetal reagents

Under the conditions of transfer hydrogenation employing an ortho-cyclometallated iridium catalyst generated in situ from [Ir(cod)Cl](2), 4-cyano-3-nitrobenzoic acid and the chiral phosphine ligand (S)-SEGPHOS, alpha-methyl allyl acetate couples to alcohols 1a-1j with complete levels of branched regioselectivity to furnish products of carbonyl crotylation 3a-3j, which are formed with good levels of anti-diastereoselectivity and exceptional levels of enantioselectivity. An identical set of optically enriched carbonyl crotylation products 3a-3j is accessible from the corresponding aldehydes 2a-2j under the same conditions, but employing isopropanol as the terminal reductant. Experiments aimed at probing the origins of stereoselection establish a matched mode of ionization for the (R)-acetate and the iridium catalyst modified by (S)-SEGPHOS, as well as reversible ionization of the allylic acetate with rapid pi-facial interconversion of the resulting pi-crotyl intermediate in advance of C-C bond formation. Additionally, rapid alcohol-aldehyde redox equilibration in advance of carbonyl addition is demonstrated. Thus, anti-diastereo- and enantioselective carbonyl crotylation from the alcohol or aldehyde oxidation level is achieved in the absence of any stoichiometric metallic reagents or stoichiometric metallic byproducts.

Catalytic, nucleophilic allylation of aldehydes with allyl acetate

A new catalytic allylation of aldehydes has been developed that employs allyl acetate as the allylating reagent. Under catalysis by ruthenium trichloride (3 mol %) in the presence of carbon monoxide (30 psi), water (1.5 equiv), and triethylamine (0.1 equiv), a wide range of aromatic, olefinic, and aliphatic aldehydes are efficiently allylated under mild conditions (70 degrees C, 24-48 h). The stoichiometric byproducts of this reaction are carbon dioxide and acetic acid.

Reactivity of IrCl(PPh3)3 with diphenylacetylene — A direct route to 1-iridaindene

The 1-iridaindene complex, Ir[C8H5(Ph-2)]Cl(PPh3)2 (2), has been prepared from the reaction of IrCl(PPh3)3 with PhC≡CPh by a novel direct cycloiridation reaction. A plausible mechanistic pathway has been suggested involving π-coordination assisted ortho- C–H activation and subsequent alkyne hydroiridation reaction to provide the five-member iridacycle.Key words: iridium, diphenylacetylene, C–H activation, cyclometallation, metallacycle.

Enantioselective iridium-catalyzed carbonyl allylation from the alcohol or aldehyde oxidation level via transfer hydrogenative coupling of allyl acetate: departure from chirally modified allyl metal reagents in carbonyl addition

Under the conditions of transfer hydrogenation employing an iridium catalyst generated in situ from [Ir(cod)Cl]2, chiral phosphine ligand (R)-BINAP or (R)-Cl,MeO-BIPHEP, and m-nitrobenzoic acid, allyl acetate couples to allylic alcohols 1a-c, aliphatic alcohols 1d-l, and benzylic alcohols 1m-u to furnish products of carbonyl allylation 3a-u with exceptional levels of asymmetric induction. The very same set of optically enriched carbonyl allylation products 3a-u are accessible from enals 2a-c, aliphatic aldehydes 2d-l, and aryl aldehydes 2m-u, using iridium catalysts ligated by (-)-TMBTP or (R)-Cl,MeO-BIPHEP under identical conditions, but employing isopropanol as a hydrogen donor. A catalytically active cyclometallated complex V, which arises upon ortho-C-H insertion of iridium onto m-nitrobenzoic acid, was characterized by single-crystal X-ray diffraction. The results of isotopic labeling are consistent with intervention of symmetric iridium pi-allyl intermediates or rapid interconversion of sigma-allyl haptomers through the agency of a symmetric pi-allyl. Competition experiments demonstrate rapid and reversible hydrogenation-dehydrogenation of the carbonyl partner in advance of C-C coupling. However, the coupling products, which are homoallylic alcohols, experience very little erosion of optical purity by way of redox equilibration under the coupling conditions, although isopropanol, a secondary alcohol, may serve as terminal reductant. A plausible catalytic mechanism accounting for these observations is proposed, along with a stereochemical model that accounts for the observed sense of absolute stereoinduction. This protocol for asymmetric carbonyl allylation transcends the barriers imposed by oxidation level and the use of preformed allyl metal reagents.

Dual-Reagent Catalysis within Ir−Sn Domain: Highly Selective Alkylation of Arenes and Heteroarenes with Aromatic Aldehydes

Reactions of arenes and heteroarenes with aromatic aldehydes proceeded smoothly in the presence of a catalytic combination of [Ir(COD)Cl]2-SnCl4 to afford the corresponding triarylmethane derivatives (TRAMs) in high yields. This 100% TRAM selective transformation is clean and eliminates the use of acid systems.

Secondary Benzylation with Benzyl Alcohols Catalyzed by A High-Valent Heterobimetallic Ir−Sn Complex

A highly efficient secondary benzylation procedure has been demonstrated using a high-valent heterobimetallic complex [Ir2(COD)2(SnCl3)2(Cl)2(mu-Cl)2] 1 as the catalyst in 1,2-dichloroethane to afford the corresponding benzylated products in moderate to excellent yields. The reaction was performed not only with carbon nucleophiles (arenes and heteroarenes) but also with oxygen (alcohol), nitrogen (amide and sulfonamide), and sulfur (thiol) nucleophiles. Mechanistic investigation showed the intermediacy of the ether in this reaction. An electrophilic mechanism is proposed from Hammett correlation.