Synthesis of Naphthopyrans via Formal (3+3)-Annulation of Propargylic (Aza)-para-Quinone Methides with Naphthols

Abstract

Herein, we report an efficient Brønsted acid-catalyzed formal (3+3)-annulation of (aza)-para-quinone methides generated in situ from propargylic alcohols with naphthol derivatives, which involves a 1,8-conjugate addition/6-endo annulation process. This protocol provides an effective method for preparing important functionalized pyranocoumarins under mild conditions.

Construction of Oxygen‐ and Nitrogen‐based Heterocycles from p‐Quinone Methides

“…A Brønsted acid (89) catalyzed synthesis of 2H-chromene derivatives (88), by exploring the reactivity of in situ generated para-quinone methides (90) from propargylic alcohols (86), has been reported by Zhang's group (Scheme 21). [41] While discussing the possible reaction pathways, the authors proposed Scheme 16. Li's approach to chiral chromene derivatives (67).…”

Formal (3 + 4)-Annulation of Propargylic p-Quinone Methides with 2-Indolylmethanols: Synthesis of Polysubstituted Indole-Fused Oxepines

“…p -Quinone methides ( p -QMs), as excellent electrophiles, have wide applications in 1,6-additions and annulations. − Among them, propargylic p -QMs with alkynyl functional substituents provide a new platform for methodological design since they have both 1,6- and 1,8-electrophilic sites. − In 2017, the Sun group realized the first example of asymmetric 1,8-addition of in situ generated propargylic p -QMs to afford chiral tetrasubstituted allenes (Scheme , a) . Then the Li group developed the 1,8-addition of propargylic p -QMs with thiazolones and azlactones .…”

“…The Wang group established a cascade 1,8-addition/Diels–Alder reaction for the construction of complex polycyclic compounds (Scheme , b) . Recently, Li and our group developed independently the Brønsted acid catalyzed (3 + 2)- and (3 + 3)-annulations of propargylic p -QMs with indoles and 2-naphthols. These works demonstrated that propargylic p -QMs were useful 3C synthons for the synthesis of five- or six-membered heterocycles (Scheme , c).…”

Brønsted Acid-Catalyzed Formal (3+3)-Annulation of Propargylic (Aza)-para-Quinone Methides with 4-Hydroxycoumarins and 1,3-Dicarbonyl Compounds

“…Although excellent pioneering work has been achieved, more exploring of propargylic (aza)- p -QMs remains significant, especially in the research field of cycloaddition reactions initiated by 1,8-conjugate addition. In the past few years, our group has been focusing on quinone methide chemistry; the formal (3+3)-annulation of propargylic (aza)- p -QMs with 1,3-dinucleophiles is rare . As shown in Scheme d, we developed an efficient (3+3)-annulation of propargylic (aza)- p -QMs with 4-hydroxy-2 H -chromen-2-one derivatives and 1,3-diketones, affording a synthetic pathway to highly functionalized pyranocoumarin and pyran derivatives.…”