Improved Synthesis of (±)-4,12-Dihydroxy[2.2]paracyclophane and Its Enantiomeric Resolution by Enzymatic Methods:  Planar Chiral (<i>R</i>)- and (<i>S</i>)-Phanol

Braddock, D. Christopher; MacGilp, Iain D.; Perry, Benjamin

doi:10.1021/jo020451x

Cited by 67 publications

(40 citation statements)

References 23 publications

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“…The absolute configuration of (S)-())-PHANOL and (R)-(+)-PHANOL were determined by X-ray diffraction analysis of (Sq,S)-2, which was identical to the data in the literature. 13 The results are shown in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

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A simple and efficient resolution of (±)-4,12-dihydroxy[2.2]paracyclophane

Jiang

Zhao

2004

Tetrahedron: Asymmetry

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Section: Resultsmentioning

confidence: 99%

“…12 More than 30 years later, enantiomerically pure PHANOL was reported by Braddock. 13 However, to the best of our knowledge, PHANOL has never been used as a ligand in asymmetric catalytic reactions. This maybe because it was limited by the shortage of enantiomerically pure PHANOL.…”

Section: Introductionmentioning

confidence: 99%

A simple and efficient resolution of (±)-4,12-dihydroxy[2.2]paracyclophane

Jiang

Zhao

2004

Tetrahedron: Asymmetry

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“…22-24 Hence, we examined the possibility of the use of bifunctional hydroxy derivatives of [2.2]paracyclophane in the allylboration reaction. In the test reactions with benzaldehyde, we used biphenols with the ortho and pseudo ortho arrangement of the hydroxy groups ((S) 16 (see Refs 18 and 19) and (R) 17, 25 were synthesized with the use of an equimolar amount of All 3 B. The cyclic structures of esters were suggested based on the almost quantitative yield of the final allylbo ration product 7.…”

Section: Methodsmentioning

confidence: 99%

Planar chiral hydroxy derivatives of [2.2]paracyclophane as auxiliaries for asymmetric allylboration

et al. 2007

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Allylboronic esters with various structures were synthesized for the first time based on [2.2]paracyclophane derivatives containing one or two hydroxy groups. It was demonstrated that these esters can be used as chiral inductors in the asymmetric allylboration of benzalde hyde. The highest enantiomeric excess of 1 phenylbut 3 en 1 ol (60%) was achieved in the reactions with acyclic bis O,O´ (paracyclophanyl) allylboronates based on (S) 4 hydroxy and (S) 12 bromo 4 hydroxy[2.2]paracyclophanes. (S) 4 Hydroxy[2.2]paracyclophane was studied by X ray diffraction.The allylboration of aldehydes is one of the most widely used approaches to the stereoselective C-C bond forma tion. 1-4 Generally, enantiomerically pure compounds (diols, diamines, sulfamides, and amino alcohols) pos sessing central 4 or (more rarely) axial chirality 5 are used for the design of reagents for the asymmetric allylboration.Earlier, 6,7 we have demonstrated for the first time that planar chiral [2.2]paracyclophane derivatives can be used in this reaction. For example, diastereomerically pure diallylborinate 2 was synthesized starting from 4 acetyl[2.2]paracyclophane (1) 8,9 (Scheme 1).Compound 2 was used in the allylboration of 4 for myl[2.2]paracyclophane (4) (de of rel (R p ,R) 4 (1 hydr oxybut 3 enyl)[2.2]paracyclophane (5) 50%) and benz aldehyde (6) (ee of 1 phenylbut 3 en 1 ol (7) was 18%). Homoallylic alcohol 3 produced in the reaction is a re cyclable auxiliary because it again gives ester 2 in the reaction with triallylborane (see Scheme 1).In alcohol 3, the hydroxy group is two bonds from the paracyclophane moiety. In the present study, we investi gated the influence of the distance between the functional group and the paracyclophane moiety on the stereochemi cal result of asymmetric allylboration of benzaldehyde. For this purpose, we examined for the first time the possi bility of designing reagents for the asymmetric allyl boration based on chiral phenols, viz., (S) 4 hydr oxy[2.2]paracyclophane (8) and (S) 12 bromo 4 hydr oxy[2.2]paracyclophane (9), in which the hydroxy group is directly fixed in the aromatic ring of [2.2]paracyclo phane.An important feature, which distinguishes phenols 8 and 9 from alcohol 3 containing two stereogenic centers, is that they contain only one (planar) chirality center, which eliminates the question about the possible coop erative effect of the planar and central chirality in the asymmetric process. Results and DiscussionSynthesis of starting phenols 8 and 9. Racemic phenol 8 was synthesized according to a known procedure. 10 To synthesize its enantiomers, we have developed 11-14 a pro cedure for the resolution of rac 8 into enantiomers through esters with (1S) (-) camphanic acid 10 (Scheme 2). 15, 16 Diastereomeric esters 10 were separated by fractional crystallization 15 followed by the preparative separation of the mother liquor by silica gel column chromatography. 16 In the present study, we improved the procedure for the isolation of enantiomers of phenol 8 from diastereo merically pure esters by us...

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“…[23][24][25] Racemic 6 was converted to the inseparable mixture of diastereomeric bromooxazolinylA C H T U N G T R E N N U N G [2.2]paracyclophanes 7 as previously described. [5] These were converted to the phenols in the same way as the pseudo-geminal analogues, above.…”

Section: Synthesis Of Pseudo-ortho Isomersmentioning

confidence: 99%

“…[5] Dibromide 6 [25] was synthesized according to the literature and resolved by preparative chiral HPLC analysis (OD column, 55 mm ID, nhexane/i-PrOH [95:5], flow rate = 30 mL min À1 , 2 bar, t R-(À) = 17 min, t S-(+) = 23 min), (Chiralcel OD column, n-hexane/iPrOH [95:5], flow rate = 1 mLmin…”

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confidence: 99%