Rapid Assembly of Functionalized Hydrodibenzofurans via Semipinacol Rearrangements

Abstract

A distinct strategy via unprecedented semipinacol rearrangements for the synthesis of functionalized hydrodibenzofurans is reported. The versatile reactivity of benzofuran-3-one as a building block enabled the convergent coupling of simple starting materials and, thus, allowed for the facile variation of R group and the construction of hydrodibenzofurans with fused rings.

Advances in the Asymmetric Synthesis of Bridged and Fused Bicyclic Acetals

“…[9] In this study, a range of fused [5,6] hemiacetal units 22 containing the hydrodibenzofurans nucleus (Scheme 1) densely functionalized with contiguous all-carbon quaternary stereogenic center via the intermediates 20 and 21 are produced. To achieve these targets via synthetic methods, a Lewis acid-mediated semipinacol rearrangement of functionalized-tertiary alcohols of type 19 was reported by Zu and coworkers.…”

“…To achieve these targets via synthetic methods, a Lewis acid-mediated semipinacol rearrangement of functionalized-tertiary alcohols of type 19 was reported by Zu and coworkers. [9] In this study, a range of fused [5,6] hemiacetal units 22 containing the hydrodibenzofurans nucleus (Scheme 1) densely functionalized with contiguous all-carbon quaternary stereogenic center via the intermediates 20 and 21 are produced. These bicyclic hemiacetals and acetals represent a structural feature of naturally occurring galanthamine-type amaryllidaceae, lunaria, and opium alkaloids.…”

Skeletal Rearrangements as Strategies for the Total Syntheses of Indole Alkaloids

“…other approaches. Isosteric structures, for example hydrodibenzofurans 7 and hydro-γ-carbolines 8 could also be successfully assembled by extensions of this strategy.…”

N-Morpholinomethyl-5-lithiotetrazole: A Reagent for the One-Pot Synthesis of 5-(1-Hydroxyalkyl)tetrazoles

“…Although N -substituted 5-metallotetrazoles have proven valuable for the introduction of the tetrazole ring system, their practicality is tempered by limited protecting group options and a susceptibility to undergo irreversible fragmentation to form lithium cyanamides 8 and dinitrogen (Scheme , B ). While Raap established the competency of 1-methyl-5-lithio-1 H -tetrazole as a nucleophile capable of C–C bond formation, Satoh developed the first 5-metallotetrazole reagent, which offered access to free 1 H -tetrazoles. , Lithiation of 1-benzyl-1 H -tetrazole ( 6 ), in this case, generated anion 7 , which, although unstable above −98 °C, underwent reaction with carbonyl compounds to form 1 , after de- N -benzylation under forcing conditions. More recently, Wiedemann has demonstrated that the magnesium and zinc derivatives of 7 display an improved thermal stability, which was attributed to the increased carbon–metal bond covalency .…”