Guanidines as Reagents and Catalysts II

214 Pages·2017·13.087 MB·English

by  Philipp Selig (eds.)

Topics in Heterocyclic Chemistry 51
Series Editors: Bert Maes · Janine Cossy · Slovenko Polanc
Philipp Selig Editor
Guanidines as
Reagents and
Catalysts II
51
Topics in Heterocyclic Chemistry
SeriesEditors:
Bert Maes, Antwerp, Belgium
Janine Cossy, Paris, France
Slovenko Polanc, Ljubljana, Slovenia
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S.V. Ley, Cambridge, UK
G. Mehta, Bangalore, India
R. Noyori, Hirosawa, Japan
L.E. Overman, Irvine, CA, USA
A. Padwa, Atlanta, GA, USA
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The series Topics in Heterocyclic Chemistry presents critical reviews on present
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covertopicsdealingwithallareaswithinheterocyclicchemistry,bothexperimental
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Philipp Selig
Editor
Guanidines as Reagents and
Catalysts II
With contributions by
V. del Amo (cid:1) R.M. Capita˜o (cid:1) C. Concello´n (cid:1) C. von Eßen (cid:1)
C.R. Go¨b (cid:1) E.R.P. Gonza´lez (cid:1) S. Herres-Pawlis (cid:1)
(cid:1) (cid:1) (cid:1) (cid:1)
H.-J. Himmel A. Hoffmann J. Mannsperger A. Metz
I.M. Oppel (cid:1) T. Ro¨sener (cid:1) R.D.E. Santo (cid:1) J. Stanek
Editor
PhilippSelig
PatheonInc.
Linz,Austria
ISSN1861-9282 ISSN1861-9290 (electronic)
TopicsinHeterocyclicChemistry
ISBN978-3-319-53012-3 ISBN978-3-319-53013-0 (eBook)
DOI10.1007/978-3-319-53013-0
LibraryofCongressControlNumber:2017936046
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Preface
Guanidines, the all-aza analogues ofcarbonic acids, representa fascinating group
ofmoleculeswithuniquechemicalandphysicalproperties.Justasthewell-known
amidines,guanidinesareexceedinglystrongBrønstedbasesandarethereforeeven
referred to as “superbases.” Moreover, guanidines can exhibit strong Lewis-basic
propertiesandthusserveaselectron-pairdonorsandligands.Afterprotonation,the
highlystabilizedguanidiniumcationisoftenusedasapowerful,bidentateH-bond
donor,capableoftightbindingandactivationofavarietyofH-bondacceptorssuch
as carbonyl groups. Finally, guanidinium cations can also be regarded as Lewis-
acidicspecieswhichcanactasp-Lewisacids.
Guanidines and their corresponding protonated species are thus capable of
exhibitingallfourbasicchemicalfunctionalities:freebasesareLewisandBrønsted
basic,whilecationsareLewisandBrønstedacidic,allconnectedbyasimpleproton
transfer.
Besides this obvious potential for synthetic applications, guanidines are also a
challengingtargetforsyntheticendeavors,mainlyduetotheirhighlybasiccharac-
ter.InthefirstvolumeofGuanidinesasReagentsandCatalysts,wethuswantedto
open with an overview of Prof. Rozas, which introduces the reader to principal
techniques for guanidine synthesis and offers a first glimpse on the potential of
guanidinesinbiologicalapplications.
Amain topic of Vol.I concerns the use ofguanidines assynthetic reagentsor,
more specifically, as organocatalysts. We are introduced into this topic with a
chapter by Prof. Ishikawa, a pioneer of guanidine organocatalysis and also the
inventor of one of the very rare examples of a commercially available guanidine
catalyst, “Ciba-G.” Ciba-G is also already highlighting the importance of multi-
functional activations in guanidine organocatalysis, a most important concept,
whichisfurtherillustratedbytheworksofProf.Takemotointhefollowingchapter.
Turningthefocusfromcatalyststructurestosyntheticapplications,Prof.Najera
willelaborateonapivotalguanidine-catalyzedreaction,i.e.,theMichaeladdition,
which makes formidable use of both the Brønsted basic and the H-bond donating
properties of the guanidine and guanidinium cation. In the following chapter,
v
vi Preface
structuresofguanidineorganocatalystsaretakentothenextlevelbyProf.Tanand
his introduction of bicyclic guanidine organocatalysts. These synthetically useful,
as well as aesthetically pleasing structures show us that highly efficient catalysis
may not be strictly contingent upon multifunctional activation, and steric effects
aroundanisolatedguanidinemoietycanbesufficienttoachieveexcellentresults.
While Prof. Tan’s work focuses on sterically rigid, mono-functional catalysts, a
quiteantipodalapproach,usinghighlyflexibleguanidineswithmultiplefunctional
groups attached, is shown to succeed just as well in the final chapter of Vol. I by
Prof.Nagasawa.
While the majority of Vol. I deals with guanidines as reagents and catalysts in
the field of organic synthesis, the potential uses of guanidines certainly go far
beyondthat.Inthesecondofthesetwovolumesafocusisplacedonthespecialized
applications of guanidines. In the first chapter Prof. Concello´n and Prof. del Amo
showustheirworksonstructurallysimpleguanidiniumsaltstoeffectivelymodify
reactions catalyzed by the classic organocatalyst L-proline, demonstrating the
designofelaboratenew catalyst structuresisnotnecessarilymandatory tobenefit
from guanidine catalysis. Guanidine organocatalysis is also involved in an indus-
triallyusefulfield,namelythenucleophilicactivationofCO asasustainableC1-
2
buildingblock.Prof.Pe´rezGonza´lezpresentsthis“green”useofguanidinecataly-
sisinthefollowingchapter.
Furtherhighlightingthepotentialusesofguanidinesoutsidetraditionalorganic
synthesis Prof. Oppel presents guanidines as ligands for super-molecular metal-
based frameworks, and the synthetic potential of such guanidinium-metal
complexes is explored by Prof. Herres-Pawlis, exemplified in their use as highly
active polymerization catalysts. Finally, at the end of this volume, Prof. Himmel
takesusfarbeyondourfocusonsyntheticorganicchemistrywithhischapteronthe
uniqueelectronicpropertiesofanionicguanidinatesandtheircomplexes.
In summary, it was our goal to show that guanidines, guanidinium salts, and
guanidinates offer a very diverse range of reactivity and thus great potential for a
widevarietyofuses.Whilestillbeingregardedasaratherexoticclassofmolecules
in the field of organocatalysis, especially in comparison to the prominent field of
proline-induced imine/enamine activation or H-bond catalysis enabled by
thioureas,the potentialofguanidinesasreagentsandcatalysts aswellasthedoor
tonovelapplicationsiscertainlywideopen.Currently,inthemid-2010s,guanidine
chemistryisahighlydynamicandrapidlydevelopingfieldofresearch,andwecan
expect exciting new developments in the future. Guanidines as reagents and
catalysts are here to stay and will continue to show up as versatile and valuable
toolsbothinandbeyondorganicchemistry.
Linz,Austria PhilippSelig
November2016
Contents
CooperativeGuanidinium/ProlineOrganocatalyticSystems. . . . . . . . . 1
CarmenConcello´nandVicentedelAmo
GuanidinesasCatalystsforDirectandIndirectCO Capture
2
andActivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
RafaelDiasdoEsp´ıritoSanto,RebecaMoniqueCapita˜o,
andEduardoRene´ Pe´rezGonza´lez
Triaminoguanidinium-BasedLigandsinSupramolecularChemistry. . . 75
CarolinavonEßen,ChristianR.Go¨b,andIrisM.Oppel
GuanidineMetalComplexesforBioinorganicChemistry
andPolymerisationCatalysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
JuliaStanek,ThomasRo¨sener,AngelaMetz,JohannesMannsperger,
AlexanderHoffmann,andSonjaHerres-Pawlis
Redox-ActiveGuanidinesandGuanidinate-SubstitutedDiboranes. . . . 165
Hans-Jo¨rgHimmel
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
vii
TopHeterocyclChem(2017)51:1–26
DOI:10.1007/7081_2015_158
#SpringerInternationalPublishingSwitzerland2015
Publishedonline:2August2015
Cooperative Guanidinium/Proline
Organocatalytic Systems
CarmenConcell(cid:1)onandVicentedelAmo
Abstract Organocatalysis is nowadays recognized as the third pillar of asym-
metric synthesis, standing next to metal catalysis and enzymatic transformations.
Proline has shown up as an ideal organocatalyst, being inexpensive and readily
available.However,thisaminoacidhasalsomanifesteditslimitations.Compared
to the chemical modification of proline, the approach through adding small
hydrogen-bond-donating cocatalysts to interact with proline is particularly attrac-
tive.Variousadditiveshavebeeninvestigatedtodate.Thischapterdisclosestheuse
ofguanidiniumsaltsasadditivesforproline,investigatedinthecourseofproline-
catalyzedaldolreactions.
Keywords Guanidinium salts (cid:129) Organocatalysis (cid:129) Proline (cid:129) Supramolecular
chemistry
Contents
1 BriefIntroductiontoOrganocatalysisandItsLimitations.................................. 2
2 AdditivesUsedforProlineinOrganocatalyzedReactions................................. 3
3 GuanidiniumSaltsasAdditivesforProlineinOrganocatalyzedReactions............... 5
3.1 Cross-AldolReactionBetweenCyclicKetonesandAromaticAldehydes.......... 5
3.2 Cross-AldolReactionBetweenChloroacetoneandAromaticAldehydes........... 17
3.3 Cross-AldolReactionBetweenα-AzidoacetoneandAromaticAldehydes.......... 18
4 ConclusionsandOutlook.................................................................... 22
References........................................................................................ 24
C.Concell(cid:1)on(*)andV.delAmo(*)
DepartamentodeQu´ımicaOrga´nicaeInorga´nica,UniversidaddeOviedo,C/Julia´nClaver´ıa8,
33006Oviedo,Spain
e-mail:[email protected];[email protected]
2 C.Concell(cid:1)onandV.delAmo
1 BriefIntroductiontoOrganocatalysisandItsLimitations
During the last decades, the demand of enantiomerically pure synthetic products
has grown exponentially. This request has made asymmetric catalysis the most
activeareaofresearchincontemporaryorganicchemistry.Illustratively,81ofthe
200blockbusterdrugsbyworldwidesalesareenantiopuresubstances.
Traditionalasymmetriccatalysisreliesontheuseoftransitionmetalcomplexes
(organometallic chemistry), or enzymes (biocatalysis). However, recently, a third
type of catalysts has appeared: the organocatalysts, with its associated discipline
asymmetric organocatalysis. This consists in the use of catalytic or substoichio-
metric amounts of simple organic molecules to carry out highly enantioselective
processes that take place in the absence of metallic elements. The use of organo-
catalysts shows a number of advantages over the utilization of transition metal
complexes: lower toxicity, low environmental impact, and absence of metallic
elements which present potential contaminants in final products, many of them
synthesizedforhumanoranimalintake.Similarly,organocatalystsdisplayadvan-
tagesovertheuseofenzymes,whichcomeatasignificantlyhigherprizeandscarce
availability.
ProjectsdealingwithorganocatalysiscanbeframedinsideGreenChemistryand
Sustainable Chemistry schemes. The concept of Sustainable Chemistry (in many
occasionssynonymouswithGreenChemistry)referstoactionsaimingtoimprove
theefficiencyintheuseofnaturalresources.Consequently,itcomprisesthedesign
andimplementationofnewchemicalprocessesandtransformationsoperatingina
moreefficient,safer,andmoreenvironmentallyfriendlyway.Havingtheintention
of pursuing those goals, Sustainable Chemistryhas been formulated in12 univer-
sally accepted principles, put forward by Anastas and Warner [1, 2]. Organo-
catalytic processes satisfy several of them: high atomic efficiency, the use of
reagentsoflowornontoxicity,littlegenerationofresidues,andtheuseofreagents
incatalyticamounts.Moreover,theE-factorvaluesoftheseprocessesareremark-
ablylow,whichisofinterestforindustry.TheE-factorquantifieshowtoxic/benign
aparticularchemicalprocessisandisexpressedastheratioofgeneratedwasterper
kilogramofproductproduced.
Theuseofsmallorganicmoleculesascatalystsinchemicaltransformationscan
be tracked back as far as the nineteenth century, to the pioneering works of Emil
Knoevenagel[3–6].Itwasn’thoweveruntiltheyear2000,withthefindingsofList,
Lerner, and Barbas on the potential of proline as a catalyst for the intermolecular
aldolreaction[7]andthoseofMacMillan[8],whentheresearchinorganocatalysis
commenced as a separate and well-defined field. Since then, the interest of the
scientific community over this discipline has been phenomenal. Nowadays, the
number of publications and literature reviews dealing with different aspects of
asymmetric organocatalysis is extraordinarily large. It is far from the objectives
of this monograph to cover the multiple and colored possibilities of this field.
Nonetheless, the following selected citations (literature reviews) can summarize
thestateoftheartofthediscipline[9–23].