Solid state asymmetric synthesis of chiral crystals of 5- and 7-membered ring ketones

Article abstract of DOI:10.3184/030823408X303970

The results of absolute asymmetric photochemical studies on 5- and 7-membered spiroketones in the solid state are described. Photolysis of 7-membered spiroketone undergoing a Norrish type II cyclisation reaction gives enantioselectivity excesses up to 93%. Irradiation of 5-membered spiroketone afforded a racemic product. The results are rationalised by the X-ray crystallographic method.

Full text of DOI:10.3184/030823408X303970

1
50ꢀ RESEARCH PAPER
MARCH,ꢀ150–151ꢀ
JOURNALꢀOFꢀCHEMICALꢀRESEARCHꢀ2008
Solid state asymmetric synthesis of chiral crystals of 5- and 7-membered
ring ketones
Xianzhu Xu, Peng Wang, Wujiong Xia and Chao Yang*
School of Municipal and Environmental Engineering and Research Academy of Science & Technology, Harbin Institute of
Technology, Harbin, Heilongjiang 150080, P. R. China
Theꢀ resultsꢀ ofꢀ absoluteꢀ asymmetricꢀ photochemicalꢀ studiesꢀ onꢀ 5-ꢀ andꢀ 7-memberedꢀ spiroketonesꢀ inꢀ theꢀ solidꢀ
stateꢀ areꢀ described.ꢀ Photolysisꢀ ofꢀ 7-memberedꢀ spiroketoneꢀ undergoingꢀ aꢀ Norrishꢀ typeꢀ IIꢀ cyclisationꢀ reactionꢀ
givesꢀenantioselectivityꢀexcessesꢀupꢀtoꢀ93%.ꢀIrradiationꢀofꢀ5-memberedꢀspiroketoneꢀaffordedꢀaꢀracemicꢀproduct.ꢀ
TheꢀresultsꢀareꢀrationalisedꢀbyꢀtheꢀX-rayꢀcrystallographicꢀmethod.
Keywords: absoluteꢀasymmetric,ꢀspiroketones,ꢀNorrishꢀtypeꢀII,ꢀsolidꢀstate,ꢀenantioselectivity
Absoluteꢀasymmetricꢀsynthesisꢀrefersꢀtoꢀtheꢀsituationꢀinꢀwhichꢀ
anꢀasymmetricꢀinductionꢀoccursꢀinꢀtheꢀabsenceꢀofꢀanꢀexternallyꢀ
1
imposedꢀ sourceꢀ ofꢀ chirality. ꢀ Suchꢀ reactionsꢀ areꢀ invariablyꢀ
hv
.
OH
carriedꢀ outꢀ inꢀ theꢀ crystallineꢀ state,ꢀ whereꢀ theꢀ asymmetricꢀ
influence governing the enantioselectivity derives from the
spontaneousꢀcrystallisationꢀofꢀanꢀachiralꢀcompoundꢀinꢀaꢀchiralꢀ
O
O
solid state
H
.
2-4
spaceꢀgroupꢀ(i.e.ꢀP2 2 2 ).
1
1 1
Duringꢀ theꢀ courseꢀ ofꢀ ourꢀ investigationꢀ onꢀ theꢀ correlationꢀ
betweenꢀ theꢀ crystalꢀ structureꢀ andꢀ solid-stateꢀ reactivity, ꢀ weꢀ
1
5
3
foundꢀ 5-,ꢀ 7-memberedꢀ ketonesꢀ (Schemeꢀ 1,ꢀ 1ꢀ andꢀ 2)ꢀ wereꢀ
crystallisedꢀ inꢀ aꢀ chiralꢀ spaceꢀ group,ꢀ P2 2 2 .ꢀ Furthermore,ꢀ
1
1 1
theꢀphotochemicalꢀprocedureꢀisꢀtheꢀconversionꢀofꢀanꢀachiralꢀ
reactantꢀtoꢀaꢀchiralꢀproduct,ꢀwhichꢀisꢀsuitableꢀforꢀasymmetricꢀ
studies.ꢀWeꢀnowꢀpresentꢀtheꢀresultsꢀofꢀourꢀinvestigations.
Theꢀketonesꢀ1ꢀandꢀ2ꢀchosenꢀforꢀstudiesꢀwereꢀsynthesisedꢀ
.
hv
O
OH
OH
solid state
H
.
5
fromꢀ commerciallyꢀ availableꢀ compoundꢀ norbornene. ꢀ
2
IrradiationꢀofꢀtheꢀaboveꢀketonesꢀinꢀacetonitrileꢀthroughꢀPyrexꢀ
usingꢀaꢀ450ꢀWꢀmedium-pressureꢀmercuryꢀlampꢀsuccessfullyꢀ
affordedꢀ theꢀ Norrishꢀ typeꢀ IIꢀ cleavageꢀ productꢀ 3ꢀ andꢀ
4
Scheme 1
6,7
cyclisationꢀproductꢀ4,ꢀrespectively. ꢀSolid-stateꢀphotolysisꢀofꢀ
ketoneꢀ1ꢀaffordedꢀaꢀracemicꢀproductꢀ3.ꢀShorteningꢀphotolyticꢀ
timeꢀ andꢀ loweringꢀ reactionꢀ temperatureꢀ haveꢀ noꢀ effectsꢀ onꢀ
improvingꢀtheꢀenantiomericꢀexcessꢀ(ee)ꢀvaluesꢀofꢀtheꢀproductꢀ
3
.ꢀ Toꢀ rationaliseꢀ theꢀ resultsꢀ obtainedꢀ inꢀ theꢀ solidꢀ state,ꢀ theꢀ
singleꢀ crystalꢀ structureꢀ ofꢀ ketoneꢀ 1ꢀ wasꢀ determinedꢀ andꢀ isꢀ
presentedꢀinꢀFig.ꢀ1,ꢀ1.ꢀForꢀphotochemicalꢀreactionsꢀinvolvingꢀ
intramolecularꢀ hydrogenꢀ atomꢀ abstraction,ꢀ itꢀ requiresꢀ
aꢀ conformationꢀ inꢀ whichꢀ theꢀ carbonylꢀ oxygenꢀ isꢀ withinꢀ
approximately 2.7 ±0.2 Å of a γ-hydrogenꢀ atom.ꢀAsꢀ itꢀ canꢀ
be seen, the distance of C=O∙∙∙∙Ha (2.478 Å) is very similar
8
to the distance of C=O∙∙∙∙Hb (2.533 Å), ꢀleadingꢀtoꢀanꢀequalꢀ
probabilityꢀinꢀabstractionꢀofꢀHaꢀandꢀHb.ꢀAsꢀaꢀresult,ꢀthereꢀisꢀnoꢀ
surpriseꢀobtainingꢀracemicꢀphotoproductꢀ3 whenꢀtheꢀreactantꢀ
1
ꢀwasꢀphotolysedꢀinꢀtheꢀsolidꢀstate.ꢀTheꢀotherꢀpossibilityꢀforꢀ
racemicꢀproductꢀ(3) isꢀthatꢀtheꢀracemisationꢀoccurredꢀinꢀtheꢀ
courseꢀofꢀketonisation.
Nowꢀ weꢀ turnꢀ toꢀ theꢀ asymmetricꢀ studiesꢀ onꢀ ketoneꢀ 2.ꢀ
Aꢀ singleꢀ crystalꢀ ofꢀ 2ꢀ wasꢀ crushedꢀ betweenꢀ twoꢀ Pyrexꢀ
microscopeꢀslides,ꢀsealedꢀinꢀpolyethyleneꢀbagsꢀunderꢀnitrogen,ꢀ
andꢀirradiatedꢀwithꢀaꢀ450ꢀWꢀmedium-pressureꢀmercuryꢀlamp.ꢀ
Followingꢀ photolysis,ꢀ theꢀ photoproductsꢀ wereꢀ analysedꢀ byꢀ
chiralꢀ HPLCꢀ toꢀ obtainꢀ theꢀ enantiomericꢀ excessꢀ (ee)ꢀ valuesꢀ
andꢀGCꢀforꢀtheꢀconversions.ꢀTheꢀresultsꢀofꢀtheꢀenantiomericꢀ
excessꢀ determinationsꢀ areꢀ summarisedꢀ inꢀ Tableꢀ 1.ꢀ Asꢀ canꢀ
beenꢀseen,ꢀtheꢀenantiomericꢀexcessesꢀvaryꢀfromꢀ23%ꢀtoꢀ93%.ꢀ
Theꢀreactionꢀatꢀroomꢀtemperatureꢀledꢀtoꢀlowꢀeeꢀ(23%),ꢀwhichꢀ
isꢀ presumablyꢀ dueꢀ toꢀ theꢀ breakdownꢀ inꢀ theꢀ crystalꢀ latticeꢀ
whenꢀtheꢀphotoproductꢀreplacesꢀtheꢀreactant.ꢀFortunately,ꢀthisꢀ
couldꢀbeꢀcompensatedꢀbyꢀloweringꢀtheꢀreactionꢀtemperatureꢀ
orꢀ decreasingꢀ theꢀ conversion.ꢀAtꢀ temperaturesꢀ muchꢀ belowꢀ
1
2
Fig. 1ꢀ ORTEPꢀrepresentationꢀofꢀtheꢀX-rayꢀcrystalꢀstructureꢀofꢀ
compoundꢀ1ꢀandꢀ2ꢀwithꢀ50%ꢀprobabilityꢀthermalꢀellipsoids.a
–
40°C,ꢀtheꢀsolid-stateꢀphotoreactionꢀbecameꢀsluggishꢀ(e.g.ꢀtheꢀ
reactionꢀwasꢀconductedꢀatꢀ-–40°Cꢀforꢀoneꢀweek,ꢀonlyꢀtraceꢀ
amountꢀofꢀphotoproductꢀwasꢀobtained).
AsꢀshownꢀinꢀFig.ꢀ(1),ꢀ2, the distance of C=O∙∙∙∙Ha (2.659Å)
is much closer than the distance of C=O∙∙∙∙Hb (3.289Å). As
aꢀ result,ꢀ bondꢀ formationꢀ betweenꢀ C1ꢀ andꢀ Caꢀ isꢀ favoured,ꢀ
affordingꢀ oneꢀ enantiomerꢀ ofꢀ photoproductꢀ 4.ꢀ Inꢀ contrast,ꢀ
formationꢀofꢀtheꢀopticalꢀantipodeꢀofꢀtheꢀphotoproductꢀobtainedꢀ
byꢀabstractionꢀofꢀHbꢀandꢀbondingꢀbetweenꢀC1ꢀandꢀCbꢀis,ꢀnotꢀ
onlyꢀunlikelyꢀonꢀdistanceꢀgrounds,ꢀbutꢀfollowingꢀabstraction,ꢀ
alsoꢀ requiresꢀ aꢀ largeꢀ amplitudeꢀ rotationꢀ ofꢀ theꢀ arylꢀ group,ꢀ
whichꢀisꢀtopochemicallyꢀforbiddenꢀinꢀtheꢀsolidꢀstate.
*
ꢀCorrespondent.ꢀEmail:ꢀxyyang@hit.edu.cn
PAPER:ꢀ08/5036

JOURNALꢀOFꢀCHEMICALꢀRESEARCHꢀ2008ꢀ 151
Table 1ꢀ Absoluteꢀasymmetricꢀstudiesꢀonꢀketoneꢀ2a
Temperature/°Cꢀ
Time/hꢀ
Conversion/%bꢀ
ee%cꢀ
[a]d
ꢀ
–5ꢀ
72ꢀ
160ꢀ
68ꢀ
21.5ꢀ
3.5ꢀ
21ꢀ
25ꢀ
79ꢀ
53ꢀ
23ꢀ
93ꢀ
92ꢀ
79ꢀ
23ꢀ
70ꢀ
–
ꢀ
ꢀ
ꢀ
ꢀ
a
–20ꢀ
ꢀ+ꢀ
ꢀ+ꢀ
ꢀ+ꢀ
–
–7ꢀ
r.t.ꢀ
r.t.ꢀ
SamplesꢀwereꢀirradiatedꢀthroughꢀPyrexꢀusingꢀaꢀ450-WꢀHanoviaꢀmedium-pressureꢀmercuryꢀlamp.
b
c
Conversion%ꢀbasedꢀonꢀGC.
DeterminedꢀbyꢀaꢀChiralpak® AS® HPLCꢀcolumnꢀwithꢀhexane/isopropanolꢀ(99:1)ꢀasꢀelutingꢀsolvent.
d
Signꢀofꢀrotationꢀofꢀmajorꢀenantiomerꢀofꢀphotoproductꢀ(4)ꢀatꢀtheꢀsodiumꢀD-line.
Currentꢀeffortsꢀinꢀasymmetricꢀstudiesꢀonꢀketonesꢀ1ꢀandꢀ2ꢀ
240.1516; Anal. Calcd for C17H20O: C, 84.96; H, 8.39. Found: C,
84.60; H, 8.55.
usingꢀ theꢀ chiralꢀ auxiliaryꢀ method1 ꢀ areꢀ ongoingꢀ inꢀ ourꢀ
0-15
General procedure for solid-state photolyses:ꢀOneꢀsingleꢀcrystalꢀofꢀ
theꢀsamplesꢀwasꢀgroundꢀandꢀsandwichedꢀbetweenꢀtwoꢀmicroscopicꢀ
slides. The sample plates were then fixed to one another with tape
andꢀplacedꢀinꢀaꢀpolyethyleneꢀbag,ꢀandꢀheat-sealedꢀunderꢀaꢀpositiveꢀ
pressureꢀ ofꢀ nitrogen.ꢀ Followingꢀ irradiation,ꢀ theꢀ samplesꢀ wereꢀ
quantitativelyꢀwashedꢀfromꢀtheꢀplatesꢀwithꢀanꢀappropriateꢀsolventꢀandꢀ
concentratedꢀin vacuo.ꢀTheꢀsamplesꢀwereꢀanalysedꢀdirectlyꢀbyꢀGCꢀforꢀ
yieldsꢀandꢀconversionsꢀand/orꢀHPLCꢀforꢀees.
group.
Experimental
General
Commercialꢀ spectralꢀ gradeꢀ solventsꢀ wereꢀ usedꢀ forꢀ photochemicalꢀ
experimentsꢀ unlessꢀ otherwiseꢀ stated.ꢀAllꢀ reactionsꢀ wereꢀ performedꢀ
underꢀ aꢀ nitrogenꢀ atmosphereꢀ unlessꢀ otherwiseꢀ noted.ꢀ Preparativeꢀ
chromatography was performed using either the flash column
methodꢀwithꢀsilicaꢀgelꢀ(particleꢀsizeꢀ230–400ꢀmesh).ꢀIRꢀspectraꢀwereꢀ
recordedꢀ onꢀ aꢀ Perkin-Elmerꢀ 1710ꢀ Fourierꢀ transformꢀ spectrometer.ꢀ
High-resolutionꢀ massꢀ spectraꢀ wereꢀ obtainedꢀ fromꢀ aꢀ Kratosꢀ MSꢀ 50ꢀ
instrumentꢀusingꢀelectronꢀimpactꢀ(EI)ꢀionisationꢀatꢀ70ꢀeV.ꢀElementalꢀ
analysesꢀwereꢀperformedꢀonꢀaꢀCarloꢀErbaꢀCHNꢀModelꢀ1106ꢀanalyser.ꢀ
We thank the financial support from the National Science
Foundationꢀ ofꢀ Chinaꢀ (50678045),ꢀ Scienceꢀ Foundationꢀ ofꢀ
Heilongjiangꢀ Provinceꢀ (E200519),ꢀ Chinaꢀ Postdoctoralꢀ
ScienceꢀFoundationꢀandꢀHeilongjiangꢀPostdoctoralꢀFinancialꢀ
AssistanceꢀandꢀtheꢀNewꢀCenturyꢀExcellentꢀTalentꢀProgramꢀofꢀ
ChineseꢀMinistryꢀofꢀEducation.
1
HꢀNMRꢀspectraꢀwereꢀobtainedꢀatꢀeitherꢀ300ꢀorꢀ400ꢀMHzꢀonꢀBrukerꢀ
1
3
AV-300ꢀ orꢀ Brukerꢀ AV-400ꢀ instruments.ꢀ Cꢀ NMRꢀ spectraꢀ wereꢀ
recordedꢀatꢀeitherꢀ75ꢀorꢀ100ꢀMHz.
Photolysis of spiroketone (1): Aꢀ solutionꢀ ofꢀ ketoneꢀ 1 (310ꢀ mg,ꢀ
.46ꢀmmol)ꢀinꢀ2:1ꢀtert-butanol/benzeneꢀ(40ꢀml)ꢀcontainingꢀanhydrousꢀ
barium oxide (15 mg) was irradiated (Pyrex filter, 450 W Hanovia
lamp)ꢀforꢀ6ꢀhꢀatꢀroomꢀtemperature.ꢀRemovalꢀofꢀsolventꢀfollowedꢀbyꢀ
1
Received 9 January 2008; accepted 29 February 2008
Paper 08/5036
doi: 10.3184/030823408X303970
silicaꢀgelꢀchromatographyꢀ(5%ꢀEt Oꢀinꢀpetroleumꢀether)ꢀgaveꢀketoneꢀ
2
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(
14ꢀ mg,ꢀ 7%)ꢀ resultingꢀ fromꢀ secondaryꢀ photocleavageꢀ ofꢀ ketoneꢀ 3.ꢀ
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HꢀNMRꢀ(CDCl ,ꢀ400ꢀMHz):ꢀδꢀ1.41ꢀ(m,ꢀ4H),ꢀ1.82ꢀ(m,ꢀ3H),ꢀ2.13ꢀ(m,ꢀ
3
9
H),ꢀ2.71ꢀ(septet,ꢀJ = 4.2ꢀHz,ꢀ2H),ꢀ2.95ꢀ(m,ꢀ2H),ꢀ3.21(m,ꢀ2H),ꢀ5.60ꢀ
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(m,ꢀ1H),ꢀ5.68ꢀ(m,ꢀ3H),ꢀ7.36ꢀ(t,ꢀJ = 7.0ꢀHz,ꢀ2H),ꢀ7.49ꢀ(d,ꢀJ = 7.5ꢀHz,ꢀ
1
3
2
7
3
1
2
7
2
8
H),7.58ꢀ(m,ꢀ2H),ꢀ7.69ꢀ(d,ꢀJ = 7.3 Hz, 2H) ppm; CꢀNMRꢀ(CDCl3,ꢀ
5ꢀMHz):ꢀδꢀ24.36,ꢀ25.29,ꢀ25.41,ꢀ26.54,ꢀ26.57,ꢀ29.12,ꢀ29.17,ꢀ29.71,ꢀ
5.19,ꢀ35.45,ꢀ51.74,ꢀ51.85,ꢀ123.08,ꢀ125.95,ꢀ126.25,ꢀ126.42,ꢀ126.48,ꢀ
26.72,ꢀ 126.79,ꢀ 127.06,ꢀ 134.37,ꢀ 137.52,ꢀ 137.54,ꢀ 154.06,ꢀ 154.09,ꢀ
07.92, 208.15 ppm; IR (neat): 3021, 2917, 1708, 1280, 1205,
ꢀ
ꢀ
4ꢀ M.ꢀ Sakamoto,ꢀ In:ꢀ Y.ꢀ Inoueꢀ andꢀ V.ꢀ Ramamurthy,ꢀ (eds)ꢀ Chiral
photochemistry,ꢀMarcelꢀDekker,ꢀNewꢀYork,ꢀ(2004)ꢀchapꢀ11.
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-1
ꢀ 6ꢀ P.ꢀ Wagnerꢀ andꢀ B.S.ꢀ Park,ꢀ Inꢀ Organic Photochemistry,ꢀ Ed.,ꢀA.ꢀ Padwa,ꢀ
53,ꢀ 660ꢀ cm ; HRMS (EI) Calcd for C H O:ꢀ 212.1201,ꢀ found:ꢀ
1
5
16
Marcel Dekker: New York, 1991; Vol. 11, Chap. 4.
12.1205.ꢀAnal.ꢀ Calcdꢀ forꢀ C H O: C, 84.87; H, 7.60. Found: C,
1
5
16
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ꢀ
7ꢀ N.C.ꢀYangꢀandꢀD.H.ꢀYang,ꢀJ. Am. Chem. Soc., 1958,ꢀ80,ꢀ2913.
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4.60; H, 7.81.
Photolysis of spiroketone (2):ꢀ Aꢀ solutionꢀ ofꢀ ketoneꢀ 2 (39ꢀ mg,ꢀ
.16 mmol) in acetonitrile (10 ml) was irradiated (Pyrex filter,ꢀ
50ꢀWꢀHanovia)ꢀforꢀ47ꢀh.ꢀRemovalꢀofꢀsolventꢀin vacuo andꢀsilicaꢀ
1
315ꢀandꢀreferencesꢀtherein.
0
4
ꢀ
9ꢀ D.ꢀBraga,ꢀS.ꢀChen,ꢀH.ꢀFilson,ꢀL.ꢀMaini,ꢀM.R.ꢀNetherton,ꢀB.O.ꢀPatrick,ꢀ
J.R.ꢀScheffer,ꢀC.ꢀScottꢀandꢀW.ꢀXia,ꢀJ. Am. Chem. Soc.,ꢀ2004,ꢀ126,ꢀ3511.
gelꢀchromatographyꢀ(10%ꢀEt Oꢀinꢀpetroleumꢀether)ꢀaffordedꢀstartingꢀ
materialꢀ 2 (17ꢀ mg,ꢀ 44%)ꢀ andꢀ cyclobutanolꢀ 4 (12 mg, 31%; 55%
basedꢀonꢀrecoveredꢀstartingꢀmaterial)ꢀasꢀaꢀcolourlessꢀoil.ꢀ HꢀNMRꢀ
2
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ꢀ
1
Soc.,ꢀ2005,ꢀ127,ꢀ2725.
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(CD Cl , 400 MHz): δ 1.68 (br, 11H), 1.99 (dt, J =ꢀ3.4,ꢀ3.2ꢀHz,ꢀ1H),ꢀ
2 2
1
3
2
.73 (m, 3H), 3.01 (m, 1H), 6.97 (m, 1H), 7.12 (m, 3H) ppm; Cꢀ
ꢀ13ꢀ C.ꢀYang,ꢀW.ꢀXia,ꢀJ.R.ꢀScheffer,ꢀM.ꢀBotoshanskyꢀandꢀM.ꢀKaftory,ꢀAngew.
NMRꢀ(CD Cl ,ꢀ75ꢀMHz):ꢀδꢀ22.42,ꢀ24.94,ꢀ27.27,ꢀ27.52,ꢀ33.58,ꢀ37.02,ꢀ
Chem. Int. Ed.,ꢀ2005,ꢀ44,ꢀ5087.
2
2
3
1
1
8.61,ꢀ46.67,ꢀ48.47,ꢀ61.17,ꢀ85.74,ꢀ125.81,ꢀ127.36,ꢀ127.42,ꢀ131.53,ꢀ
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2006,ꢀ8,ꢀ388.
41.54, 143.71 ppm; IR (neat): 3445, 2948, 2931, 2863, 1448, 1077,
-1
030,ꢀ893ꢀcm ; HRMS (EI) Calcd for C H O:ꢀ240.1514,ꢀfound:ꢀ
1
7
20
PAPER:ꢀ08/5036