Enantioselective Cascade Oxa‐Michael–Michael Reactions of 2‐Hydroxynitrostyrenes with Enones Using a Prolinol Thioether Catalyst

Abstract

The efficient simultaneous activation of cyclohexenones or simple alkyl acyclic enones and 2‐hydroxynitrostyrenes was realized by using a prolinol thioether catalyst. Thus, a highly chemo‐, diastereo‐ and enantioselective synthesis of functionalized tetrahydroxanthenones and chromanes with up to three contiguous stereocenters was developed.magnified image

Tools and techniques for solvent selection: green solvent selection guides

“…15 acyclic carbonates are not sufficiently polar to be considered a direct substitute for classic dipolar aprotic solvents. Despite being considered as 'problematic' , p-cymene has no red shaded scores, and as a renewable hydrocarbon is well placed to substitute toluene and other aromatic solvents [79][80][81][82][83][84]. Cyclic carbonates [70,85], and Cyrene [69], suffer in the environmental assessment because of their high boiling points, but offer clear health advantages over classical dipolar aprotic solvents (Fig.…”

Recent advances in organocatalytic asymmetric oxa-Michael addition triggered cascade reactions

“…In view of the good result reported by Enders' group, similar work for the construction of functionalized tetrahydroxanthenones and chromans was finished by Xu's group 18 in 2014. Under the catalysis of prolinol thioether catalyst 28 and 4-trifluoromethylbenzoic acid additive, nitrovinylphenols 21 and cyclohexenones 27 gave the products tetrahydroxanthenones 29 with excellent yields (up to 98%) and stereoselectivities (up to >20 : 1 dr and 99% ee) in brine at room temperature (Scheme 9a).…”

Dually activated Michael-Michael-acetalization cascade: facile and highly diastereoselective construction of tetrahydro-6-hydroxyl-6H-benzo[c]chromen-9-one polycyclic scaffold

“…9 Generally, the current cascade sequences were initiated by oxaMichael reaction of phenol moiety and enals followed by another Michael addition to assemble ring B firstly. 10 And ring C was then installed via the subsequent reaction sequence. Despite these encouraging successes on developing synthetic protocol of the tricyclic core, the exploration of novel cascade reaction sequence by modulating the chemical reactivity of the substrate is still highly demanding, which would permit the efficient construction of the diverse tricyclic core structures including hemiacetal and lactone analogs, due to their presence in natural products or key synthetic intermediates (Fig.…”