N-Heterocyclic carbene-triggered transition-metal-free synthesis of 2,3-disubstituted benzofuran derivatives

Abstract

An NHC-triggered, transition-metal-free strategy for the efficient synthesis of 2,3-disubstituted benzofuran derivatives in moderate to excellent yields from aryl or alkyl aldehydes and o-quinone methides has been developed. This method features mild reaction conditions, operational simplicity, broad substrate scope and convergent assembly.

Application of Naphthylindole-Derived Phosphines as Organocatalysts in [4 + 1] Cyclizations of o-Quinone Methides with Morita–Baylis–Hillman Carbonates

“…A survey of the literature only revealed several examples of [4 + 1] cyclizations of o -QMs with one-carbon synthons (Scheme ). − In these cases, sulfur ylides (eq 3), pyridinium methylides (eq 4), in situ generated oxy-phosphonium enolates (eq 5), aldehydes (eq 6), ammonium ylides (eq 7), and bromomalonates or 3-chlorooxindoles (eq 8) were successfully utilized as one-carbon synthons to perform [4 + 1] cyclizations with o -QMs. Despite these elegant approaches, [4 + 1] cyclizations of o -QMs with one-carbon synthons are still rather limited, which requires the selection of suitable one-carbon synthons and the specific design of [4 + 1] cyclizations of o -QMs.…”

“…A survey of the literature only revealed several examples of [4 + 1] cyclizations of o-QMs with one-carbon synthons (Scheme 2). 8−14 In these cases, sulfur ylides (eq 3), 8 pyridinium methylides (eq 4), 9 in situ generated oxyphosphonium enolates (eq 5), 10 aldehydes (eq 6), 11 ammonium ylides (eq 7), 12 and bromomalonates 13 or 3chlorooxindoles 14 (eq 8) were successfully utilized as onecarbon synthons to perform [4 + 1] cyclizations with o-QMs.…”

Facile Chemoselective synthesis of 2‐(2‐(Methoxycarbonyl)‐3‐oxo‐2,3‐dihydrobenzofuran‐2‐yl)benzoic acids and 3H,3’H‐Spiro[benzofuran‐2,1′‐isobenzofuran]‐3,3′‐dione derivatives

“…Besides medicinal and bilogical properties, substituted benzofurans find applications such as fluorescent sensor, oxidant, antioxidants, brightening agents and agriculture As a result of these important properties, many research groups have investigated various methods for the synthesis and structural modification of benzofuran ring with the purpose of exploring their diverse biological activities Thus, benzofuran moiety can be taken as the lead compound for the synthesis of novel derivatives with a variety of chemical and biological activities …”

PPh3-Triggered Tandem Synthesis of 2,3-Disubstituted Benzofuran Derivatives from o-Quinone Methides with Acyl Chlorides

“…Owing to their high reactivity and rearomatization propensity, o -QMs can readily undergo Michael addition with appropriate nucleophiles as well as cycloaddition or cyclization with a variety of dienophiles or dipolars, respectively, which offers an efficient approach for the purpose of synthesizing valuable oxygen-containing heterocycles . In this case, [4 + 1] cycloaddition reactions of o -QMs were recently achieved to generate benzofuran derivatives using different C1 units (Scheme ), including active methylene compounds with leaving groups (a), in situ generated oxyphosphonium enolates (b), aldehydes (c), allylic ylide species (d), and carbenes (e) . Despite these elegant advances, compared with [4 + 2] and [4 + 3] cycloadditions of o -QMs, [4 + 1] cycloadditions are still rather limited to carbon nucleophiles and mainly rely on the dual nature (nucleophilic and electrophilic) of the C position.…”