Intermolecular and Intramolecular α-Amidoalkylation Reactions Using Bismuth Triflate as the Catalyst

Abstract

Bismuth(III) triflate was found to promote the formation of stable cyclic N-acyliminium species in remarkable catalytic amounts (1 mol %). The alpha-amidoalkylation process seems to be effective in intermolecular and intramolecular manners leading to alpha-substituted lactams and heterocyclic systems containing azacycles, respectively. By comparing our results with those obtained with the classical Lewis acids as catalysts, it was evidenced clearly that the use of bismuth(III) triflate had been efficient for nearly all alpha-acetoxy lactams we used, except for N-acyliminium precursors bearing a sulfur atom. Also, the process seems to be easy, general, and clean, having diastereoselectivity comparable to protocols using classical Lewis acids and resulting in the formation of polyheterocyclic systems in good to excellent yields (64-99% in acetonitrile as solvent).

Strategies Based on Aryllithium and N‐Acyliminium Ion Cyclizations for the Stereocontrolled Synthesis of Alkaloids and Related Systems

“…[28] In this example, as in other related ones reported previously, [44] the stereochemical outcome is the result of attack from the aromatic ring anti to the acetoxy group. Scheme 22. However, the introduction of bulkier groups at this α-position does not necessarily lead to higher levels of diastereoselection.…”

“…[27] In this context, bismuth(III) triflate has been found to promote the formation of cyclic acyliminium ions in remarkably low amounts (1 mol-%), suitable for both inter- and intramolecular reactions. [28] As depicted in Scheme 12, Bi(OTf) 3 -catalyzed intramolecular cyclizations of the acetoxylactams 39, obtained from the imides 38, took place in acetonitrile at room temperature, in an improvement on the results previously obtained for these substrates with TFA. [29] Although the Bi(OTf) 3 is tolerant towards the presence of an N,O-acetal functionality in 39 (X = O) and also of methoxy groups (R = OCH 3 ), substrates containing an S,N-acetal function (X = S) undergo cleavage of the S-C linkage under the reaction conditions.…”

“…[29] Although the Bi(OTf) 3 is tolerant towards the presence of an N,O-acetal functionality in 39 (X = O) and also of methoxy groups (R = OCH 3 ), substrates containing an S,N-acetal function (X = S) undergo cleavage of the S-C linkage under the reaction conditions. [28] Scheme 12.…”

Bismuth(III) bromide in organic synthesis. A catalytic method for the allylation of tetrahydrofuranyl and tetrahydropyranyl ethers

“…Daich and co-workers have reported a bismuth triflate-catalyzed intermolecular α-amidoalkylation of a variety of α-acetoxylactams with silanes and enoxysilanes. 6 Floreancig and co-workers report a very efficient BiBr3 mediated allylation of a lactol to yield a tetrahydropyranyl alcohol. 7 This reaction was a key step in their studies directed toward the construction of Leucascandrolide A, an antifungal macrolide.…”

Association of Intramolecular Furan Diels-Alder Reaction and N-Acylim­­i­n­ium Alkylation for the Synthesis of Pentacyclic Precursor of Aromathecins

“…Access to 6 and 8 was easily accomplished in a few steps from the known acetoxy lactam 4 13 based on an a-amidoalkylation process via the stable Nacyliminium cation followed by a Wittig-Horner reaction.…”