Phase‐Transfer‐Catalyzed Oxazirid­ine‐Mediated Hydroxylative Phenol and Naphthol Dearomatization

Abstract

Abstract:A new methodology for the dearomative orthohydroxylation of substituted phenolic substrates is reported. In the presence of a phase-transfer catalyst and a base, N-sulfonyloxaziridines react with phenols to give the corresponding 6-

Site‐selective Oxidative Dearomatization of Phenols and Naphthols into ortho‐Quinols or Epoxy ortho‐Quinols using Oxone as the Source of Dimethyldioxirane

“…If we consider the oxidative dearomatization of phenol 1 a with oxaziridines or hypervalent iodine reagents–– (Scheme a), only the cyclodimer 3 a was obtained. When the reaction of 1 a is performed with Oxone/NaHCO 3 /CH 3 CN, as source of singlet oxygen ( 1 O 2 ), followed by reduction with Na 2 S 2 O 3 , the para ‐quinol 4 a was formed (Scheme b) .…”

“…Moreover, ortho-quinols and their [4 + 2] cyclodimers also constitute the main structural elements of many natural products (Figure 1b) such as wasabidienone B 1 , [3] epoxysorbicillinol [4] and grandifloracin. [5] The transformation of phenols and naphthols into the corresponding ortho-quinol derivatives has been investigated by using (oxo)-or (peroxo)metal species, [6] selenium compounds, [7] oxaziridines, [8] and hypervalent iodine compounds. [9] Nevertheless, new and environmentally friendly strategies for their siteselective synthesis under mild conditions still represents a synthetic challenge.…”

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

“…Hereby both, approaches relying on either asymmetric metal- or organocatalysis, have been well-investigated already [ 105 – 122 ]. In the field of non-covalent asymmetric organocatalysis, chiral H-bonding catalysis [ 37 , 121 – 122 ] and chiral phase-transfer ion-pairing catalysis [ 110 – 119 ] turned out to be extremely powerful.…”

“…Very recently, Toullec and co-worker reported the use of phase-transfer catalysts to carry out the dearomatization of phenol and naphthol derivatives 25 via ortho -hydroxylation to obtain the highly-functionalized targets 26 [ 119 ]. Hereby oxaziridines 23 were found to be the best-suited hydroxylating agents.…”

Gold‐Catalyzed Dearomatization of 2‐Naphthols with Alkynes

“…In the realm of catalytic dearomatization reactions, naphthol derivatives are facing growing attention, resulting in the preparation of densely functionalized and stereochemically defined naphthalen‐2(1 H )‐one, which is a molecular motif featured in numerous naturally occurring and bioactive compounds (Figure ). The catalytic dearomatization of 2‐naphthols found elegant applications with the use of strongly activated electrophiles through the realization of new C−X (X: oxidative approach, for example, hydroxylation, amination,, thiolation, and halogenation) as well as C−C bonds at the C(1) position . In the latter case, the use of strongly activated carbon‐based electrophiles is commonly required to access mild reaction conditions and synthetically useful selectivity.…”