Ytterbium triflate-catalyzed conjugate addition of β-ketoesters to activated 1,4-naphthoquinones

Dihydronaphthofurans: synthetic strategies and applications

“…The reaction was carried out in CH 2 Cl 2 at room temperature for 12 h yielded 61% of a mixture of cis and trans (20 : 80) 2,3-dihydronaphtho[1,2-b]furan derivatives 28 (Scheme 9). 29 Alla et al 30 noted that one-pot reaction of 2-amino-4H-pyran derivatives 29 with N-chlorosuccinimide and a base (piperidine or aqueous KOH) in alcohol medium at room temperature for 8-9 h gave dihydronaphthofurans 30 in 68-90% yields. Plausible mechanism for the formation of 30 has been arrived at Scheme 10.…”

Ytterbium Triflate: A Green Catalyst

“…The adducts 19 were obtained in excellent yields. 9 (F) Selective Oxidative Cross-Coupling: Yb(OTf) 3 is used along with an achiral or a chiral copper complex in the synthesis of naphthol derivatives 22. Employing this binary catalyst system the cross-coupling proceeded in a specific manner.…”

“…(E) Conjugate Addition of b-Ketoesters to Activated Quinones: Kimpe and co-workers reported the conjugated addition of various b-ketoesters 17 to activated 1,4-naphthoquinones 18 mediated by catalytic amounts of Yb(OTf) 3 . The adducts 19 were obtained in excellent yields 9. (F) Selective Oxidative Cross-Coupling: Yb(OTf) 3 is used along with an achiral or a chiral copper complex in the synthesis of naphthol derivatives 22.…”

Copper(II) Bromide/Boron Trifluoride Etherate‐Cocatalyzed Cyclization of Ketene Dithioacetals and p‐Quinones: a Mild and General Approach to Polyfunctionalized Benzofurans

“…Nevertheless, the method based on the conjugate addition and sequential cyclization of quinones with active alkenes in the presence of an over‐stoichiometric amount of Lewis or Brønsted acids provides an alternative route to the benzofuran skeleton 5a–f. The Yb(OTf) 3 ‐catalyzed conjugate addition of β‐keto esters to activated 1,4‐naphthoquinones was developed for the facile synthesis of benzofurans recently 5g. While each of the above approaches2–5 represents an important advance towards the objective of an efficient method for the construction of benzofurans, the synthesis of densely functionalized benzofurans is limited and remains a challenge.…”