Conspectus Merging the characteristics of transfer hydrogenation and carbonyl addition, we have developed a new class of catalytic enantioselective C-C bond formations. In these processes, hydrogen transfer between alcohols and π-unsaturated reactants generates carbonyl-organometal pairs that combine to deliver products of addition. Based on this mechanistic paradigm, lower alcohols are converted directly to higher alcohols in the absence of premetalated reagents or discrete alcohol-to-carbonyl redox reactions. In certain cases, due to a pronounced kinetic preference for primary vs secondary alcohol dehydrogenation, diols and higher polyols are found to engage in catalytic stereo- and site-selective C-C bond formation - a capability that further enhances efficiency by enabling skeletal construction events without extraneous manipulations devoted to the installation and removal of protecting groups. While this Account focuses on redox-neutral couplings of alcohols, corresponding aldehyde reductive couplings mediated by 2-propanol were developed in parallel for most catalytic transformations reported herein. Mechanistically, two distinct classes of alcohol C-H functionalizations have emerged, which are distinguished by the mode of pronucleophile activation; specifically, processes wherein alcohol oxidation is balanced by (a) π-bond hydrometalation or (b) C-X bond reductive cleavage. Each pathway offers access to allylmetal or allenylmetal intermediates and, therefrom, enantiomerically enriched homoallylic or homopropargylic alcohol products, respectively. In the broadest terms, carbonyl addition mediated by premetalated reagents has played a central role in synthetic organic chemistry for well over a century, however, the requisite organometallic reagents pose issues of safety, require multistep syntheses and generate stoichiometric quantities of metallic byproducts. The concepts and catalytic processes described in this Account, conceived and developed wholly within the author’s laboratory, signal a departure from the use of stoichiometric organometallic reagents in carbonyl addition. Rather, they reimagine carbonyl addition as a hydrogen auto-transfer process or cross-coupling in which alcohol reactants, by virtue of their native reducing ability, drive generation of transient organometallic nucleophiles and, in doing so, serve dually as carbonyl proelectrophiles. The catalytic allylative and propargylative transformations developed thus far display capabilities far beyond their classical counterparts and their application to the total synthesis of type I polyketide natural products have evoked a step-change in efficiency. More importantly, the present data suggest that diverse transformations traditionally reliant on premetalated reagents may now be conducted catalytically without stoichiometric metals. This Account provides the reader and potential practitioner with a catalog of enantioselective alcohol-mediated carbonyl additions – a user’s guide, 10-year retrospective, and foundation for future work in this ...

The use of gaseous allene as an allyl pronucleophile in enantioselective aldehyde reductive coupling is described. Notably, using the same antipode of chiral ligand, (S)-tol-BINAP, an inversion of enantioselectivity is observed for allene versus allyl acetate pronucleophiles. Experimental and computational studies corroborate intervention of diastereomeric π-allyliridium-C,O-benzoate complexes, which arise via allene hydrometalation (from a pentacoordinate iridium hydride) versus allyl acetate ionization (from a square planar iridium species).

Cyclometallated π‐allyliridium C,O‐benzoates modified with (S)‐tol‐BINAP, which are stable to air, water, and SiO2, catalyze highly enantioselective N‐allylations of indoles and related azoles. This reaction complements previously reported metal‐catalyzed indole allylations in that complete levels of N versus C3 and branched versus linear regioselectivity are observed.

The first examples of amphiphilic reactivity in the context of enantioselective catalysis are described. Commercially available π-allyliridium C,O-benzoates, which are stable to air, water and SiO chromatography, and are well-known to catalyze allyl acetate-mediated carbonyl allylation, are now shown to catalyze highly chemo-, regio- and enantioselective substitutions of branched allylic acetates bearing linear alkyl groups with primary amines.

The air and water stable π-allyliridium C,O-benzoate modified by (S)-tol-BINAP, (S)-Ir-II, catalyzes highly regio- and enantioselective Tsuji-Trost type aminations of racemic branched alkyl-substituted allylic acetates using primary or secondary (hetero)aromatic amines. Specifically, in the presence of (S)-Ir-II (5 mol%) in DME solvent at 60-70 °C, α-methyl allyl acetate 1a (100 mol%) reacts with primary (hetero)aromatic amines 2a-2l (200 mol%) or secondary (hetero)aromatic amines 3a-3l (200 mol%) to form the branched products of allylic amination 4a-4l and 5a-5l, respectively, as single regioisomers in good to excellent yield with uniformly high levels of enantioselectivity. As illustrated by the conversion of heteroaromatic amine 3m to adducts 6a-6g, excellent levels of regio- and enantioselectivity are retained across diverse branched allylic acetates bearing normal alkyl or secondary alkyl substituents. For reactants 3n-3p, which incorporate both primary and secondary aryl amine moieties, regio- and enantioselective amination occurs with complete site-selectivity to furnish adducts 7a-7c. Mechanistic studies involving amination of the enantiomerically enriched deuterium labelled acetate 1h corroborate C-N bond formation via outer-sphere addition.