Microwave-Induced Synthesis of Aromatic Heterocycles

103 Pages·2012·6.14 MB·English

by  Abdul Rauf

SpringerBriefs in Molecular Science
Green Chemistry for Sustainability
Series Editor
Sanjay K. Sharma
For furthervolumes:
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Abdul Rauf Nida Nayyar Farshori
•
Microwave-Induced
Synthesis of Aromatic
Heterocycles
123
AbdulRauf Nida Nayyar Farshori
Department of Chemistry B-1,Liberty Homes
Aligarh MuslimUniversity OppositeAbdullah College
Aligarh MarrisRoad
India Aligarh 202002
e-mail: [email protected] India
e-mail: [email protected]
ISSN 2191-5407 e-ISSN 2191-5415
ISBN 978-94-007-1484-7 e-ISBN978-94-007-1485-4
DOI 10.1007/978-94-007-1485-4
SpringerDordrechtHeidelbergLondonNewYork
(cid:2)TheAuthor(s)2012
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Preface
Heterocyclesformbyfarthelargestoftheclassicaldivisionsoforganicchemistry
and are of immense importance biologically, industrially and indeed to the func-
tioning of any developed human society. The majority of pharmaceuticals and
biologically active agrochemicals are heterocycles. The importance of heterocy-
clesprovidesanewbasisforthedevelopmentofnewmethodsfortheirsynthesis.
Due to the strengthening environment regulations and safety concerns, there is a
needofnewinnovative,environmentallyfriendlysyntheticroutesforsynthesizing
important heterocyclic compounds. Such synthesis can be designed using micro-
wave technology. We therefore planned to publish a mini book that will include
themicrowaveassistedsynthesisofheterocycliccompounds.Althoughtherearea
large number ofpapersontheselectedsubject,however,wecan onlyincorporate
the recent references. We nevertheless extend our apologies to all the scientists
whose research findings could not be cited or discussed in our mini book. The
present bookshall beofinteresttoallorganicchemistsaswellaspharmaceutical
and environmental chemists.
Abdul Rauf
Nida Nayyar Farshori
v

Contents
1 Introduction to Microwave Chemistry. . . . . . . . . . . . . . . . . . . . . 1
1.1 Conventional Heating Methods Versus Microwave Heating. . . 2
1.2 Theory of Microwave Synthesis. . . . . . . . . . . . . . . . . . . . . . 3
1.3 Equipments Used in Microwave Synthesis. . . . . . . . . . . . . . . 4
1.4 Safety Precautions in Microwave Synthesis. . . . . . . . . . . . . . 5
1.5 Coupling of Microwave Radiation with Solvent
Free Heterocyclic Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . 6
1.6 Application of Microwave Activation in
Heterocyclic Chemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Oxazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3 Thiazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4 Oxazolines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5 Oxadiazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6 Pyrazoles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
7 Imidazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
vii
viii Contents
8 Triazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
9 Triazines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
10 Benzimidazoles, Benzothiazoles and Benzoxazoles . . . . . . . . . . . . 75
10.1 Benzimidazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
10.2 Benzothiazoles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
10.3 Benzoxazoles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Chapter 1
Introduction to Microwave Chemistry
Abstract Formorethanacenturyheterocycleshaveconstitutedoneofthelargest
areas of research in organic chemistry. The heterocyclic moieties are of excep-
tionalinterestinthepharmaceuticalindustryastheymakeupacorepartofseveral
drugs. The importance of heterocycles provides a significant basis for the devel-
opment of new methods for their synthesis. Further, due to the strengthening
environmental regulations and safety concerns, the industries are in need of new
innovative,environmentalfriendlyalternateroutesforsynthesizingthetherapeutic
and pharmacological important heterocyclics are desired. This environmentally
benign synthesis can be easily designed using microwave methodology. The
microwaves induce rapid heating and avoid the harsh classical conditions,
resultingintheformationofcleanerproducts.Thefirstchapterthusdealswiththe
microwavetheory,latestdevelopmentsininstrumentationtechnology,thevarious
microwave technologies used for synthesis.
Keywords Introduction (cid:2) Theory (cid:2) Equipments (cid:2) Safety precautions (cid:2) Hetero-
cyclic synthesis
High-speed microwave synthesis has attracted a considerable amount of attention
inrecentyears[1].Thereisanincreasedinterestintechnologiesandconceptsthat
facilitate more rapid synthesis and screening of chemical substances to identify
compounds with appropriate qualities. One such high-speed technology is a
microwave-assistedorganicsynthesis(MAOS).Sincethefirstreportsontheuseof
microwave heating to accelerate organic chemical transformations by the groups
ofGedye[2]in1986, morethan2,000articleshavebeenpublishedintheareaof
MAOS [3]. The MAOS technology facilitates the discovery of novel pathways,
because the extreme reaction conditions attainable by microwave heating some-
times lead to unusual reactivity that cannot always be duplicated by conventional
heating.Theinitialslowuptakeofthetechnologyinthelate1980sandearly1990s
has been attributed to its lack of controllability and reproducibility, coupled with
A.RaufandN.N.Farshori,Microwave-InducedSynthesisofAromatic 1
Heterocycles,SpringerBriefsinGreenChemistryforSustainability,
DOI:10.1007/978-94-007-1485-4_1,(cid:2)TheAuthor(s)2012