Efficient Coupling Reaction of Quinone Monoacetal with Phenols Leading to Phenol Biaryls

Abstract

A simple and efficient synthesis of phenol biaryls by the cross‐couplings of quinone monoacetals (QMAs) and phenols is reported. The Brønsted acid catalytic system in 1,1,1,3,3,3‐hexafluoro‐2‐propanol was found to be particularly efficient for this transformation. This reaction can be extended to the synthesis of various phenol biaryls, including sterically hindered biaryls, with yields ranging from 58 to 90 % under mild reaction conditions and in a highly regiospecific manner.

Regioselective Construction of Functionalized Biarylols by Fe(OTf)3‐Catalyzed Direct Arylation of 1‐Diazonaphthalen‐2(1H)‐ones and Their Fluorescence Properties

“…Recently, biaryls bearing phenol or 2‐naphthols have been used extensively as versatile ligands and starting materials for asymmetric transformations . Representative methods for the construction of biaryls bearing phenol or 2‐naphthols include the hypervalent iodine(III)‐catalyzed oxidative phenol–arene cross‐coupling reaction [(1); Scheme ], K 2 S 2 O 8 ‐mediated oxidative coupling of 2‐naphthols with phenols (2), Brønsted acid catalyzed or organocatalytic coupling reaction of quinone, quinone monoacetal, or iminoquinone with phenols or 2‐naphthol (3), and chiral metal complex catalyzed oxidative homocoupling of 2‐naphthols (4) . Although a number of synthetic approaches for the preparation of racemic and chiral biaryls bearing phenols and 2‐naphthols have been developed, more facile and efficient protocols are still highly desirable as new synthetic strategies.…”

Selective [5,5]‐Sigmatropic Rearrangement by Assembly of Aryl Sulfoxides with Allyl Nitriles

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Aromatic [5,5]-sigmatropic rearrangement is an appealing protocol for accessing 1,4-substituted arenes.H owever,s uch ap rotocol has not been well utilized in organic synthesis because of the difficulties in the synthesis of the substrates,s electivity issues,a nd limited substrate scope. Described herein is an ew [5,5]-sigmatropic reaction utilizing readily available aryl sulfoxides and allyl nitriles.This reaction features mild reaction conditions,high chemo-and regioselectivity,e xcellent functional-group compatibility,a nd broad substrate scope.Computational studies suggest that the success of the reaction can be attributed to the selective electrophilic assembly of the rearrangement precursors,i nw hich al inear -C = C = N-linkage favors [5,5]-sigmatropic rearrangement over the competitive [3,3]-sigmatropic rearrangement.

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“…The [3,3]-sigmatropic rearrangement is apowerful process in organic synthesis,a nd an umber of named reactions have been developed based on this rearrangement. [1,2] Thesuccess of this process can be mainly attributed to its inherently high chemo-and regioselectivities.I ns harp contrast, [5,5]-sigmatropic rearrangement reactions,t hough also thermally allowed by the Woodward-Hoffmann rules,h ave not attracted that much attention and have been rarely reported. [3][4][5] TheC laisen-type rearrangement of phenyl dienyl ethers to the para-functionalized phenols is ac lassic [5,5]-sigmatropic rearrangement reaction [Scheme 1a, Eq.…”

“…(1)]. [3] Although the reaction was well developed with good para regioselectivity by Naruta in 1986, it has not received much attention, [3a] probably because of the limited substrate scope.T he benzidine rearrangement represents another important [5,5]-sigmatropic reaction [Scheme 1a,Eq. (2)].…”

“…(2)]. [4] Thei ntriguing reaction pattern has triggered extraordinary efforts of chemists.H owever, in addition to the desired para-benzidine,t he reaction also affords side products such as ortho-benzidine, ortho-semidine, para-semi-dine,a nd diphenyline,t hus raising selectivity issues.T he addition of phenol to iminoquinone acetals also proceeds by [5,5]-sigmatropic rearrangement to form aremote C À Nbond [Scheme 1a,E q. (3)].…”