Enantioselective dialkylzinc-mediated alkynylation, arylation and alkenylation of carbonyl groups

Synthesis of Novel 3-Deoxy-3-thio Derivatives of d-Glucosamine and Their Application as Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde

A series of novel thio-derivatives of d-glucosamine has been synthesized using double inversion procedures at the C3 atom. New compounds were applied as ligands for the diethylzinc addition to benzaldehyde and the products of the addition were obtained with a low to good enantiomeric ratio. The direction and the level of the asymmetric induction were highly dependent on the type of protecting groups on the nitrogen and sulfur atoms.

Leveraging the Stereochemical Complexity of Octahedral Diastereomeric-at-Metal Catalysts to Unlock Regio-, Diastereo-, and Enantioselectivity in Alcohol-Mediated C-C Couplings via Hydrogen Transfer

Experimental and computational studies illuminating the factors that guide metal-centered stereogenicity and, therefrom, selectivity in transfer hydrogenative carbonyl additions of alcohol proelectrophiles catalyzed by chiral-at-metal-and-ligand octahedral d6 metal ions, iridium(III) and ruthenium(II), are described. To augment or invert regio-, diastereo-, and enantioselectivity, predominantly one from among as many as 15 diastereomeric-at-metal complexes is required. For iridium(III) catalysts, cyclometalation assists in defining the metal stereocenter, and for ruthenium(II) catalysts, iodide counterions play a key role. Whereas classical strategies to promote selectivity in metal catalysis aim for high-symmetry transition states, well-defined low-symmetry transition states can unlock selectivities that are otherwise difficult to achieve or inaccessible.

Visible-Light-Driven α-Aminoalkyl Radical-Mediated C(sp3)-C(sp) Cross-Coupling of Iodoalkanes and Alkynyl Bromides

We herein report a simple protocol for metal-free cross-coupling between unactivated alkyl iodides and terminal alkynyl bromides promoted by visible light. The salient features of this transformation are the utilization of an organic photocatalyst and commercially available tri-n-butylamine as a reductant. This protocol couples a variety of unactivated iodoalkanes containing different functional groups and with a variety of terminal alkynyl bromides under mild reaction conditions to afford the substituted alkynes in good yields.

Enantioselective Metal-Catalyzed Reductive Coupling of Alkynes with Carbonyl Compounds and Imines: Convergent Construction of Allylic Alcohols and Amines

The use of alkynes as vinylmetal pronucleophiles in intermolecular enantioselective metal-catalyzed carbonyl and imine reductive couplings to form allylic alcohols and amines is surveyed. Related hydrogen auto-transfer processes, wherein alcohols or amines serve dually as reductants and carbonyl or imine proelectrophiles, also are cataloged, as are applications in target-oriented synthesis. These processes represent an emerging alternative to the use of stoichiometric vinylmetal reagents or Nozaki-Hiyama-Kishi (NHK) reactions in carbonyl and imine alkenylation.

Facile Synthesis and Utilization of Bis(o-phosphinophenyl)zinc as Isolable PZnP-pincer Ligands Enabled by Boron-Zinc Double Transmetallation

Bis(o-phosphinophenyl)zinc derivatives were successfully synthesized by the reaction of o-phosphinophenylboronates with dimethylzinc via boron-zinc double transmetallation. The transmetallation was significantly accelerated by the presence of the ortho PR2 substituent to...

Highly Regio- and Enantioselective Reductive Coupling of Alkynes and Aldehydes via Photoredox Cobalt Dual Catalysis

A Co-catalyzed highly regio- and enantioselective reductive coupling of alkynes and aldehydes has been developed under visible light photoredox dual catalysis. A variety of enantioenriched allylic alcohols have been obtained by using unsymmetrical internal alkynes and commercially available catalyst, chiral ligand, and reagents. It is noteworthy that this approach has considerable advantages, such as excellent regio- (>95:5 for >40 examples), stereo- (up to >95:5 E/Z), and enantioselectivity (92-99% ee, >35 examples) control, mild reaction conditions, broad substrate scope, and good functional group compatibility, making it a great improvement to enantioselective alkyne-aldehyde reductive coupling reactions.

Five-Step Enantioselective Synthesis of Islatravir via Asymmetric Ketone Alkynylation and an Ozonolysis Cascade

A 5-step enantioselective synthesis of the potent anti-HIV nucleoside islatravir is reported. The highly efficient route was enabled by a novel enantioselective alkynylation of an α,β-unsaturated ketone, a unique ozonolysis-dealkylation cascade in water, and an enzymatic aldol-glycosylation cascade.

Visible light promoted coupling of alkynyl bromides and Hantzsch esters for the synthesis of internal alkynes

A metal-free visible light promoted C(sp3)-C(sp) coupling reaction of alkynyl bromides and Hantzsch esters was developed, giving internal alkynes with primary, secondary, tertiary alkyl or other functional groups in good to high yields.

Catalytic asymmetric synthesis of 3-aryl phthalides enabled by arylation–lactonization of 2-formylbenzoates

The catalytic asymmetric synthesis of 3-aryl phthalides through an asymmetric arylation–lactonization is enabled by a B/Zn exchange reaction.

Copper-catalyzed enantioselective alkynylation of pyrazole-4,5-diones with terminal alkynes

A copper-catalyzed enantioselective alkynylation between pyrazole-4,5-diones and terminal alkynes is developed, and both enantiomers of chiral propargylic alcohols can be achieved by using the ligand illustrated and its diastereomer.

Metal-Free Synthesis of Functionalized Tetrasubstituted Alkenes by Three-Component Reaction of Alkynes, Iodine, and Sodium Sulfinates

An operationally simple, efficient, and metal-/peroxide-free three-component reaction of alkynes, iodine, and sodium sulfinates has been developed for the construction of highly functionalized tetrasubstituted alkenes. Iodo- and sulfonyl-containing tetrasubstituted alkenes, such as vinyl ketones, allylic alcohols, and conjugated enynes, could be obtained regio- and stereoselectively in up to 96% yield.

Catalytic Enantioselective Addition of Organozirconium Reagents to Aldehydes

A catalytic enantioselective addition reaction of alkylzirconium species to aromatic aldehydes is reported. The reaction, facilitated by a chiral nonracemic diol ligand complex with Ti(OⁱPr)₄, proceeds under mild and convenient conditions, and no premade organometallic reagents are required since the alkylzirconium nucleophiles are generated in situ by hydrozirconation of alkenes with the Schwartz reagent. The methodology is compatible with functionalized nucleophiles and a broad range of aromatic aldehydes.

Dinuclear zinc complex catalyzed asymmetric methylation and alkynylation of aromatic aldehydes

A general AzePhenol dinuclear zinc catalytic system has been successfully developed and introduced into the asymmetric addition of dimethylzinc and alkynylzinc to aromatic aldehydes.

DFT calculations of the molecular structures and vibrational spectra of dimethylzinc and dimethylcadmium complexes with bidentate nitrogen ligands

The structures and vibrational spectra of dimethylzinc and dimethylcadmium complexes with o-phenanthroline (PHEN), 2,2′-bipyridine (BIPY), and tetramethylethylenediamine (TMED) have been calculated by DFT methods. The unexpected deviations in the dihedral angles between the plane of the o-phenanthroline ligand and the planes of the dimethyl-metal groups are due to low wavenumber twisting vibrations and the previously unknown locations of the metal–nitrogen stretching motions have been established. The results indicate that the ligands are not strongly bound, suggesting that the complexes may indeed be useful nontoxic precursors to Me2Zn and Me2Cd for use in the electronics industry.

Total Synthesis of Chiral Falcarindiol Analogues Using BINOL-Promoted Alkyne Addition to Aldehydes

An enantioselective total synthesis of chiral falcarindiol analogues from buta-1,3-diyn-1-yltriisopropylsilane is reported. The key step in this synthesis is BINOL-promoted asymmetric diacetylene addition to aldehydes. The two chiral centers of the falcarindiol analogues can be produced by using the same kind of catalyst with high selectivity, and the final product can be obtained in only six steps.