Potassium tert-Butoxide-Mediated Condensation Cascade Reaction: Transition Metal-Free Synthesis of Multisubstituted Aryl Indoles and Benzofurans

Abstract

An efficient and facile method to synthesize valuable disubstituted 2-aryl indoles and benzofurans in good yields has been demonstrated, based on a tert-butoxide-mediated condensation reaction involving a vinyl sulfoxide intermediate. Products are obtained from N- or O-benzyl benzaldehydes using dimethyl sulfoxide as a carbon source. The methodology features a wide functional group tolerance and transition metal-free environment. Preliminary mechanistic studies suggest that the reaction involves a tandem aldol reaction/Michael addition/dehydrosulfenylation/isomerization sequence through an ionic protocol.

Synthesis of Terminal N‐Vinylazoles from Aromatic Aldehydes, DMSO, and Azoles Based DMSO as Terminal Carbon Synthon

“…On the basis of the above experimental results and in combination with previous literature, [15–18] a reasonable reaction mechanism was proposed using benzaldehyde 1 a and indole 2 a as an example and outlined in Scheme 4. Initially, benzaldehyde 1 a reacted with DMSO under base conditions to give the styryl sulfoxide A through an aldol condensation reaction.…”

“…On the basis of the above experimental results and in combination with previous literature, [15][16][17][18] a reasonable reaction mechanism was proposed using benzaldehyde 1 a and indole 2 a as an example and outlined in…”

Synthesis of Non‐Terminal Alkenyl Ethers, Alkenyl Sulfides, and N‐Vinylazoles from Arylaldehydes or Diarylketones, DMSO and O, S, N‐Nucleophiles

“…[b] Isolated yield. Based on the above experimental results and combination with previous literature, [14] a reasonable reaction mechanism was proposed using benzaldehyde 1 a and methanol 2 a as an example and outlined in Scheme…”

Regio- and stereoselective base-catalyzed assembly of 6-methylene-5-oxaspiro[2.4]heptanones from alkynyl cyclopropyl ketones

“…Our preliminary experiments revealed that the commonly used procedures to generate anionic species from alkyl alkynyl ketones with the use of DABCO 6 or PPh Therefore, we have chosen an inexpensive and easy-to-handle potassium tert-butoxide/DMSO catalytic system ( pK a ∼ 32) 12 to activate the model ketone 1a. To our delight, when ketone 1a was treated with t-BuOK (10 mol%) in DMSO at room temperature for 120 min (Table 1, entry 1), the desired oxa-spirocyclopropane derivative 2a was obtained in 10% yield.…”