Transition-Metal-Free С–С Coupling of 5,7-Dihydroxybenzopyrones with Quinoxalones and Pteridinones

Abstract

A new synthetic protocol for nucleophilic substitution of hydrogen­ in quinoxalones and pteridinones by the action of 5,7-di­hydroxycoumarins and related m-dihydroxybenzene compounds has been developed. The C–C coupling reaction proved to proceed smoothly under rather mild conditions, thus giving the corresponding C–H functionalized products in good yields. The advantages of this environmentally benign protocol are high regio- and chemoselectivity, and an easy workup procedure. Direct incorporation of the coumarin moiety into the pyrazine ring in pteridines or quinoxalines provides a short pathway to pyrazine-coumarin hybrid compounds.

Cross‐Dehydrogenative Coupling Reactions between Phenols and Hetarenes: Modern Trends in Cross‐Coupling Chemistry of Phenols

“…For instance, Khalymbadzha and co-workers developed a novel synthetic protocol for the nucleophilic substitution of hydrogen in quinoxalones and pteridones by using 5,7dihydroxycoumarins. [91] Cross-coupling reactions proceeded under mild conditions exclusively at the C8 position of the coumarin system and resulted in the formation of pyrazine-coumarin hybrid compounds. In the case of 7-nitro-quinoxalone, the S N H products were obtained in moderate yields via a two-step procedure consisting of the addition of 5,7-dihydroxycoumarin to the double bond of 7-nitro-quinoxalone (Scheme 35i) and the subsequent oxidation of the corresponding σ Hadducts with p-chloranil in DMF (Scheme 35ii).…”

“…However, in the case of pteridin-4-one (R=H), the oxidative coupling products were obtained in moderate yields via a one-step reaction involving TFA. [91] Khalymbadzha et al [92] showed that 5,7-dihydroxycoumarins can undergo nucleophilic addition to sand as-triazines in the same manner as diazines [91] to form stable σ H -adducts in yields of up to 97%. p-Chloranil enabled the aromatisation of the dihydrotriazine σ H -adducts, affording the oxidative coupling products in good yields.…”

“…Interestingly, 5,7‐dihydroxycoumarins also possess a resorcinol ring and may act as a nucleophilic agent in the same manner as phenol. For instance, Khalymbadzha and co‐workers developed a novel synthetic protocol for the nucleophilic substitution of hydrogen in quinoxalones and pteridones by using 5,7‐dihydroxycoumarins [91] . Cross‐coupling reactions proceeded under mild conditions exclusively at the C8 position of the coumarin system and resulted in the formation of pyrazine‐coumarin hybrid compounds.…”

“…The interaction of 5,7‐dihydroxycoumarins with pteridin‐4,6‐dione in TFA also leads to stable σ H ‐adducts, which can be converted into the S N H products using p ‐chloranil (Scheme 36). However, in the case of pteridin‐4‐one (R=H), the oxidative coupling products were obtained in moderate yields via a one‐step reaction involving TFA [91] …”

“…Khalymbadzha et al [92] . showed that 5,7‐dihydroxycoumarins can undergo nucleophilic addition to s ‐ and as ‐triazines in the same manner as diazines [91] to form stable σ H ‐adducts in yields of up to 97%. p ‐Chloranil enabled the aromatisation of the dihydrotriazine σ H ‐adducts, affording the oxidative coupling products in good yields.…”