Studies on the Intermolecular Hydroarylation of N-Ts- or N-Ac-Protected Indoles and 2,3-Allenoates

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

3-Methylbuta-1,2-dien-1-ylphosphonic acid derivatives (phosphorylallenes) [X₂(O=)P–CR=C=CMe₂, X = Cl, OMe, NR₂, or SAr] undergo intramolecular cyclization into the corresponding 1,2-oxaphospholium ions in the Brønsted superacid TfOH. These cations have been thoroughly studied by means of NMR spectroscopy. The hydrolysis of superacidic solutions of these species afforded cyclic phosphonic acids and other phosphorus-containing compounds. Contrary to Brønsted acids, 3-methylbuta-1,2-dien-1-ylphosphonic dichloride [Cl₂(O=)P–HC=C=CMe₂] reacted with the Lewis acid AlCl₃ in an intermolecular way forming noncyclic intermediates, which were investigated by NMR spectroscopy and DFT calculations. Hydrolysis of these species resulted in the formation of phosphoryl-substituted allyl alcohols and 1,3-butadienes. A strong coordination of the oxygen of the P=O group with AlCl₃ prevented the formation of cyclic 1,2-oxaphospholium ions and played a crucial role in the different reactivity of such phosphorylallenes under the action of Brønsted or Lewis acids. Apart from that, the reaction of dichlorophosphorylallenes with arenes and AlCl₃ led to products of hydroarylation of the allene system, phosphoryl-substituted alkenes and/or indanes. This is the first example of a Lewis acid-promoted intermolecular hydroarylation of allenes bearing electron-withdrawing substituents. Plausible reaction mechanisms have been proposed on the basis of the investigated reactions, and NMR analysis and DFT studies of the intermediate cationic species.

Gold(I)-Catalysed Hydroarylation of 1,3-Disubstituted Allenes with Efficient Axial-to-Point Chirality Transfer

Hydroarylation of enantioenriched 1,3-disubstituted allenes has the potential to proceed with axial-to-point chirality transfer to yield enantioenriched allylated (hetero)aryl compounds. However, the gold-catalysed intermolecular reaction was previously reported to occur with no chirality transfer owing to competing allene racemisation. Herein, we describe the development of the first intermolecular hydroarylations of allenes to proceed with efficient chirality transfer and summarise some of the key criteria for achieving high regio- and stereoselectivity.

Synthesis, molecular and crystal structure analysis of 1-(4-Methylbenzenesulfonyl)indole-3-carbaldehyde and DFT investigation of its rotational conformers

Two independent molecules that differ in terms of rotation about the central S-N bond comprise the asymmetric unit of the title compound 1. The molecules have a V-shape with the dihedral angles between the fused ring system and benzene ring being 79.08(6)° and 72.83(5)°, respectively. The packing is mostly driven by π···π interactions occurring between the tolyl ring of one molecule and the C₆ ring of the indole fused ring system of the other. DFT and IRC calculations for these and related 1-(arylsulfonyl)indole molecules showed that the rotational barrier about the S-N bond between conformers is within the 2.5–5.5 kcal/mol range. Crystal data for C₁₆H₁₃NO₃S (1): Mr = 299.33, space group Pna2₁, a = 19.6152(4) Å, b = 11.2736(4) Å, c = 12.6334(3) Å, V = 2793.67(13) ų, Z = 8, Z' = 2, R = 0.034.