Indium Triiodide Catalyzed Reductive Functionalization of Amides via the Single-Stage Treatment of Hydrosilanes and Organosilicon Nucleophiles

Sequential KOtBu/FeCl3-catalyzed reductive phosphonylation of tertiary amides for the synthesis of α-amino phosphonates and phosphines

A simple, mild and efficient sequential KO^tBu/FeCl₃-catalyzed reductive phosphonylation of tertiary amides is herein described. This process first involved the KO^tBu-catalyzed selective semi-reduction of tertiary amides to hemiaminal intermediates by TMDS (1,1,3,3-tetramethyldisiloxane) and then the FeCl₃-catalyzed nucleophilic addition of the hemiaminal intermediates to phosphonates, which allowed the straightforward synthesis of α-amino phosphonates in moderate to good yields. This method applied well to amides and lactams that bear no strong acidic α-hydrogens, and various functional groups, including methoxy, methylthio, cyano, halogen, and heterocycles, could be tolerated.

KOtBu-Mediated Reductive Cyanation of Tertiary Amides for Synthesis of α-Aminonitriles

A simple, mild, catalyst-free, and efficacious KO^tBu-mediated reductive cyanation reaction of tertiary amides under hydrosilylation conditions has been described. A series of α-aminonitriles is obtained in moderate to high yield with good functional group tolerance. The reaction works well with a readily available amide substrate, a cheap and versatile base KO^tBu, and a commercially available hydrosilane (EtO)₃SiH and is convenient for workup and purification.

Diastereoselectivity Switch in the Pd(0)/InI-Mediated Reactions of β-Lactams with Aldehydes: An Entry into Nonracemic Semiprotected (3E)-2,6-Enediols

The switch from N-methylimidazole (N-MI) to the Et₃N N-ligand efficiently alters diastereoselectivity in Pd(0)/InI-mediated allylations of aldehydes with β-lactam-derived organoindiums. As a result, (3E)-selective allylations and crotylations of a variety of aliphatic and (hetero)aromatic aldehydes with differently substituted chiral ε-amido-allylindiums were developed. Depending on the relative β-lactam configuration, the reactions occur under kinetic or thermodynamic control, with effective remote 1,5- or 1,4,5-asymmetric induction to afford a diversity of previously unavailable (3E)-2,5-syn-2,6-anti-, (3E)-2,5-anti-2,6-anti-, and (3E)-2,5-anti-2,6-syn-substituted enediols, amino alcohols, and homoallylic alcohols in modest to high yields and with moderate to excellent diastereoselectivity. The effect of the N-ligand as well as β-lactam and aldehyde structures on the yield and stereoselectivity was investigated.

Ruthenium-Catalyzed Reductive Arylation of N-(2-Pyridinyl)amides with Isopropanol and Arylboronate Esters

A new three-component reductive arylation of amides with stable reactants (iPrOH and arylboronate esters), making use of a 2-pyridinyl (Py) directing group, is described. The N-Py-amide substrates are readily prepared from carboxylic acids and PyNH₂ , and the resulting N-Py-1-arylalkanamine reaction products are easily transformed into the corresponding chlorides by substitution of the HN-Py group with HCl. The 1-aryl-1-chloroalkane products allow substitution and cross-coupling reactions. Therefore, a general protocol for the transformation of carboxylic acids into a variety of functionalities is obtained. The Py-NH₂ by-product can be recycled.

Acyclic Remote 1,5- and 1,4,5-Stereocontrol in the Catalytic Stereoselective Reactions of β-Lactams with Aldehydes: The Effect of the N-Methylimidazole Ligand

The application of the N-methylimidazole ( N-MI) ligand in the Pd(0)/InI-promoted allylations of aldehydes with β-lactam-derived organoindiums enables the reaction of azetidin-2-ones with diversely substituted allyl moieties, inert under previously reported conditions. As a result, allylations and crotylations of a variety of aromatic and aliphatic aldehydes with previously unavailable chiral ε-amido-allylindiums bearing α-, β-, or γ-substituted allyl fragments were developed. The reactions occur under thermodynamic control with a highly efficient remote 1,5- or 1,4,5-stereocontrol to afford a diversity of (3 Z)-2,5- anti-2,6- syn- or (3 Z)-2,5- syn-2,6- anti-substituted enediols, aminoalcohols, and homoallylic alcohols in moderate to high yields and with an excellent diastereoselectivity. A detailed study on the effect of the β-lactam and aldehyde structures and chirality on the yield and stereochemistry in the products was carried out.

Copper-catalyzed electrophilic amination using N-methoxyamines

Copper-catalyzed electrophilic amination of a triarylboroxin using an N-methoxyamine to give quick access to a variety of anilines was reported. The reaction was especially useful for syntheses of functionalized anilines when combined with our previously reported nucleophilic addition to N-methoxyamides.

Iridium-Catalyzed Reductive Strecker Reaction for Late-Stage Amide and Lactam Cyanation

A new iridium-catalyzed reductive Strecker reaction for the direct and efficient formation of α-amino nitrile products from a broad range of (hetero)aromatic and aliphatic tertiary amides, and N-alkyl lactams is reported. The protocol exploits the mild and highly chemoselective reduction of the amide and lactam functionalities using IrCl(CO)[P(C₆ H₅ )₃ ]₂ (Vaska's complex) in the presence of tetramethyldisiloxane, as a reductant, to directly generate hemiaminal species able to undergo substitution by cyanide upon treatment with TMSCN (TMS=trimethylsilyl). The protocol is simple to perform, broad in scope, efficient (up to 99 % yield), and has been successfully applied to the late-stage functionalization of amide- and lactam-containing drugs, and naturally occurring alkaloids, as well as for the selective cyanation of the carbonyl carbon atom linked to the N atom of proline residues within di- and tripeptides.

Sequential Addition Reaction of Sulfanylmethyllithiums and Grignard Reagents to Thioformamides Leading to the Formation of 2-Phenyl-2-sulfanylethyl Tertiary Amines

The reaction of sulfanylmethyllithiums generated from benzylsulfanes and n-BuLi with N,N-dimethylthioformamide followed by the addition of Grignard reagents gave 2-phenyl-2-sulfanyl tertiary amines in moderate to good yields. A range of Grignard reagents involving primary alkyl, aryl, vinyl, and alkynyl Grignard reagents were used. Two carbon-carbon bond-forming reactions were achieved through a one-pot reaction. The reaction showed good to high diastereoselectivity, particularly with alkynyl Grignard reagents.

Chemoselective reductive nucleophilic addition to tertiary amides, secondary amides, and N-methoxyamides

As the complexity of targeted molecules increases in modern organic synthesis, chemoselectivity is recognized as an important factor in the development of new methodologies. Chemoselective nucleophilic addition to amide carbonyl centers is a challenge because classical methods require harsh reaction conditions to overcome the poor electrophilicity of the amide carbonyl group. We have successfully developed a reductive nucleophilic addition of mild nucleophiles to tertiary amides, secondary amides, and N-methoxyamides that uses the Schwartz reagent [Cp2 ZrHCl]. The reaction took place in a highly chemoselective fashion in the presence of a variety of sensitive functional groups, such as methyl esters, which conventionally require protection prior to nucleophilic addition. The reaction will be applicable to the concise synthesis of complex natural alkaloids from readily available amide groups.