HNTf₂-Catalyzed Synthesis of Hydrodibenzofurans by an Epoxidation/Semipinacol Rearrangement Cascade

Abstract

Described here is a highly efficient synthesis of hydrodibenzofurans, an important structural unit lacking general access, in particular, with contiguous quaternary stereocenters. In the presence of HNTf2 as the superior catalyst and mCPBA as an oxidant, the readily available styrene substrates underwent a one-pot cascade process comprising epoxidation, semipinacol rearrangement, and hemiketal formation to furnish hydrodibenzofurans with good efficiency and diastereoselectivity.

Euphnerins A and B, Diterpenoids with a 5/6/6 Rearranged Spirocyclic Carbon Skeleton from the Stems of Euphorbia neriifolia

“…The carbonyl group of C-1 in compound 3 may be reduced to a carbinol group to generate i, and ii could be obtained by epoxidation of the double bond of i. Owing to the instability of the oxirane ring of ii, the ring would be cleaved via protonation to create a C-5 carbocation. Subsequent ring contraction involving the C-1−C-10 bond would form spiro intermediate v. 33 The loss of a proton in hydroxy group v would afford the C-10 carbonyl group in 1 and 2; a dehydration/reduction may then convert 1 into 2.…”

Recent development and applications of semipinacol rearrangement reactions

“…Apart from allylic alcohols, a cascade process of ortho -hydroxy styrenes 4 was devised by Sun's group for the synthesis of hydrodibenzofurans 6 ( Scheme 2b ). 20 The formation of an ortho -quinone methide intermediate 5 was suggested after the epoxidation, which would trigger the ring-expansion of the resulting cyclopentanol to generate 6 with two consecutive quaternary stereocenters.…”

Triflamides and Triflimides: Synthesis and Applications

“…As a catalyst/co-catalyst based on the Tf 2 Nsalts of metals (Au, Ag, Fe, Li, Ca), triflimide has found application in a wide range of addition reactions, cycloaddition, intramolecular cyclization, CH-amidation, etc. Tf 2 NH is often used as an additive to the reaction medium, for example, in the synthesis of spiroheteropolycyclic compounds [8,9] and nitrogen-containing heterocycles [10], in catalytic Molecules 2022, 27, 5201 2 of 33 (3 + 2)-annelation [11], in the oxidative synthesis of hydrodibenzofurans [12] and in condensed 2,8-O,O-or O,N-bicyclo [3.3.1]nonanes [13]. The triflimide anion is a counterion for the production of low-melting ionic liquids, used to stabilize nanoparticles, which are used in various fields, including medicine, sensors, optics and the aerospace industry [14,15].…”