A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

• Olusesan K. Koleoso,
• Matthew Turner,
• Felix Plasser and
• Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

• radical addition, using photoredox catalysis, to allenamides and allencarbamates is reported. This transformation synthesizes N-acyl-N’-aryl-N,N’-allylaminals, and proceeds by a conjugated N-acyliminium intermediate that previously has principally been generated by electrophilic activation methods. The

• radical adds to the central carbon of the allene giving a conjugated N-acyliminium that undergoes nucleophilic addition by arylamines and alcohols. Keywords: allenamide; allene; intermolecular; N-acyliminium; photoredox; Introduction Allenamides (Scheme 1, 1) and their congeners have attracted

• innovative transformations, including cycloadditions [5][6][7][8][9], intramolecular cyclizations and intermolecular addition reactions [10][11][12][13][14][15][16][17][18], as well as the use of the allenamide building block in natural product synthesis [1]. Addition reactions of allenamides, which can also

Why base-catalyzed isomerization of N-propargyl amides yields mostly allenamides rather than ynamides

• Armando Navarro-Vázquez

Beilstein J. Org. Chem. 2015, 11, 1441–1446, doi:10.3762/bjoc.11.156

• furnish N-allenyl compounds (allenamides/allencarbamates) or further evolve to N-alkynyl compounds (ynamides or yncarbamates). The particular fate of this reaction varies from experiment to experiment and there is no clear rule for predicting the reaction outcome for a particular structure. With the

• predict the experimentally observed behavior for several examples from the literature. Keywords: allenamide; DFT; isomerization; ynamide; Introduction Allenamides [1][2] and ynamides [3][4][5] have become useful functional groups for organic chemistry synthesis in the last years. Reduced electron pair

• Hsung and coworkers, “…This poses an interesting fundamental question as to why the thermodynamically more stable ynamide … was not found if these isomerizations involved an equilibration mechanism…” [2]. The available experimental data strongly suggest that allenamides do not always convert to ynamides

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• 1,1-disubstituted olefins proceeded smoothly to give functionalized cyclopentenes in satisfactory yields with up to 98% ee (Scheme 3). That study extended the substrate scope of known asymmetric phosphine-catalyzed [3 + 2] annulation reactions to diverse heteroatom-substituted olefins and allenamides

• . Nitrogen-, phosphorus-, oxygen-, and sulfur-substituted olefins and allenamides were compatible with these B4-catalyzed reactions. Fu’s results provided useful hints for further expansion of the substrate scope. Using B2 as the chiral catalyst, Marinetti and co-workers also developed several asymmetric [3

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• allenamides [70] or allenyl ethers [71] participate as two-carbon atom components in several gold-catalyzed [4 + 2] cycloadditions with dienes. The racemic version of the reaction between allenamides and dienes, which is efficiently promoted by AuCl or the cationic gold catalyst Au9/AgSbF6, was translated

• into a enantioselective version by using a novel chiral gold complex Au14, featuring a triazole unit embedded in a rigid axially chiral cyclic frame (Scheme 11) [72]. The catalyst generated from Au14 and AgNTf2 was able to promote the [4 + 2] cycloaddition between allenamides 16 and conjugated dienes

• catalyst provides a gold–allyl cationic species of type IX, which is the species undergoing the cycloaddition process with the diene [73]. Simple alkenes do also react with gold-activated allenamides to provide cyclobutane products, formally resulting from a [2 + 2] cycloaddition. Thus, independent

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• -indolyl allenamides. Amidation reaction of 1-allyl-2-indolecarboxamides. Intramolecular cyclization of N-benzoylindole. Intramolecular alkenylation/carboxylation of alkenylindoles. Intermolecular alkenylation/carboxylation of 2-substituted indoles. Mechanistic investigation of the cyclization

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• allenamides 61 and conjugated dienes 62 (Scheme 32); a process that provided a straight entry to a variety of differently substituted cyclohexenes 63, and took place with excellent regio- and diastereoselectivity [109]. Almost simultaneously a (4 + 2) cycloaddition between allenyl ethers and dienes was also

• ) Cycloadditions of allenenes [87][99]. (3 + 2) versus (2 + 2) Cycloadditions of allenenes [106]. Gold(I)-catalyzed intermolecular (4 + 2) cycloaddition of allenamides and acyclic dienes [109]. Acknowledgements Our work is supported by the Spanish MICINN [SAF2010-20822-c02, and Consolider-Ingenio 2010 (CSD2007

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• obtained in all cases. A similar Markovnikov hydroamination [59] could also be achieved via an intermolecular hydroamination of allenamides 123 with arylamines under mild AuPPh3OTf catalysis conditions to furnish allylamino (E)-enamides stereoselectively (Scheme 22). Hesp and co-workers have identified a

• and mild synthesis of enamides (193–196) by a gold-catalyzed nucleophilic addition to allenamides 191 (Scheme 36) [87]. For example, treatment of allenamide and 1-methylindole with 5.0 mol % of PPh3AuNTf2 in CH2Cl2 at room temperature gave the corresponding enamide in 83% yield. Gold-catalyzed direct

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• -hydrogen shifts from allenamides are described. These 1,3-hydrogen shifts could be achieved thermally or they could be promoted by the use of Brønsted acids. Under either condition, these processes are highly regioselective in favour of the α-position, and highly stereoselective in favour of the E

• -configuration. In addition, 6π-electron electrocyclic ring-closure could be carried out with 3-amido-trienes to afford cyclic 2-amido-dienes, and such electrocyclic ring-closure could be rendered in tandem with the 1,3-hydrogen shift. Keywords: allenamides; 2-amido-dienes; 3-amido-trienes; electrocyclic ring

• ][41][42][43], for earlier studies on allenamides see [44][45][46]) can open the door to construct synthetically useful amido-dienes (for a review on the synthesis of enamides see [47], for reviews on the chemistry of dienamides see [48][49][50], for reviews on the chemistry of 2-amino or 2-amido