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Chalcogenides As Organocatalysts Eoghan M Chem. Rev. 2007, 107, 5841−5883 5841 Chalcogenides as Organocatalysts Eoghan M. McGarrigle,† Eddie L. Myers,‡ Ona Illa,† Michael A. Shaw,† Samantha L. Riches,† and Varinder K. Aggarwal*,† School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom Received August 21, 2007 Contents 4.1.2. Catalysis via Ylide Formation from a 5859 Carbene Source 1. Introduction 5841 4.1.3. Applications in Synthesis 5860 1.1. Scope 5842 4.2. Selenide-Catalyzed Cyclopropanations 5860 2. Epoxidation 5842 4.3. Telluride-Catalyzed Cyclopropanations 5861 2.1. Sulfide-Catalyzed Epoxidations 5843 4.4. Summary of Chalcogenide-Catalyzed 5861 2.1.1. Catalysis via Sulfide Alkylation/ 5843 Cyclopropanations Deprotonation 5. Sulfide-Catalyzed Chromene Synthesis 5862 2.1.2. Catalysis via Ylide Formation from a 5846 6. Telluride-Catalyzed Olefin Synthesis 5862 Carbene Source I: Diazo Compounds 6.1. Te-ylide Olefination and Related Reactions 5862 2.1.3. Ylide Formation from a Carbene Source 5847 II: N-Tosylhydrazone Salts 6.2. Telluride-Catalyzed Dehalogenation and 5864 Related Reactions 2.1.4. Ylide Formation from a Carbene Source 5849 − − III: Simmons−Smith Reagent 7. Morita Baylis Hillman-type Reactions 5864 2.1.5. Origin of Diastereoselectivity in S-Ylide 5849 7.1. Introduction 5864 Epoxidations 7.2. Aldehydes and Activated Ketones as 5865 2.1.6. Origin of Enantioselectivity in 5850 Terminal Electrophiles Sulfide-Catalyzed Asymmetric 7.2.1. TiCl4 and Chalcogenide 5865 Epoxidations 7.2.2. BX3 (X ) F, Cl, Br) and Chalcogenide 5869 2.1.7. Applications in Synthesis 5852 7.3. Oxonium and Iminium Ions as Terminal 5870 2.2. Selenide-Catalyzed Epoxidations 5852 Electrophiles 2.3. Telluride-Catalyzed Epoxidations 5853 8. Miscellaneous Reactions Involving 1,4-Addition of 5874 2.4. Summary of Chalcogenide-Catalyzed 5853 Chalcogenide Epoxidations 8.1. Halohydroxyalkylation of Electron-Deficient 5874 3. Aziridination 5853 Alkynes 3.1. Sulfide-Catalyzed Aziridinations 5853 8.2. Synthesis of â-Substituted Silyl Enol Ethers 5875 3.1.1. Catalysis via Sulfide Alkylation/ 5853 9. Radical-Polar Crossover Chemistry 5876 Deprotonation 9.1. Radical Cyclization Followed by Oxidative 5876 3.1.2. Catalysis via Ylide Formation from a 5854 Quench Carbene Source I: Diazo Compounds 9.1.1. Reactions of 2-Allyloxy Benzene 5876 3.1.3. Ylide Formation from a Carbene Source 5855 Diazonium Salts with TTF II: N-Tosylhydrazone Salts 9.1.2. Tandem Cyclizations 5877 3.1.4. Ylide Formation from a Carbene Source 5855 9.1.3. Extension to Indolines 5878 III: Simmons−Smith Reagent 9.1.4. Application in Synthesis 5878 3.1.5. Origin of Diastereoselectivity in 5856 9.2. Radical Translocation 5878 Sulfide-Catalyzed Aziridinations 9.2.1. Benzamide Substrates 5879 3.1.6. Origin of Enantioselectivity in 5857 9.2.2. Anilide Substrates 5879 Sulfide-Catalyzed Asymmetric 9.2.3. Ether Substrates 5880 Aziridinations 9.3. TTF-Related Reagents 5880 3.1.7. Applications in Synthesis 5857 9.4. Summary of Radical-Polar Crossover 5880 3.1.8. Summary of Chalcogenide-Catalyzed 5857 Chemistry Aziridinations 10. Conclusions 5880 4. Cyclopropanation 5858 11. Abbreviations 5881 4.1. Sulfide-Catalyzed Cyclopropanations 5858 12. Acknowledgements 5881 4.1.1. Catalysis via Sulfide Alkylation/ 5858 Deprotonation 13. References 5881 * To whom correspondence should be addressed. Phone: +00-44-117- 9546315. Fax: +00-44-117-9298611. E-mail: [email protected]. 1. Introduction † University of Bristol. ‡ Current Address: Department of Biochemistry, University of Wisconsins In this review, we describe the many roles chalcogenides Madison, 433 Babcock Drive, Madison, Wisconsin 53706-1544. play as organocatalysts. Chalcogens, or the oxygen family, 10.1021/cr068402y CCC: $65.00 © 2007 American Chemical Society Published on Web 12/12/2007 5842 Chemical Reviews, 2007, Vol. 107, No. 12 McGarrigle et al. Eoghan M. McGarrigle was born in Dublin, Ireland. He studied chemistry Ona Illa was born and educated in Barcelona, Spain. She obtained her at University College Dublin, where he obtained his B.Sc. degree in 1998. first degree from the Universitat Auto`noma de Barcelona in 2000. She He carried out his doctoral studies under the supervision of Dr. Declan then undertook her Ph.D. studies with Professors Rosa Maria Ortun˜o and Gilheany and was awarded his Ph.D. for his thesis on metal(salen) Vicenc¸ Branchadell in the same university, working on the synthesis of chemistry in 2003. He then worked as a postdoctoral fellow in the group phosphino(silyl)carbenes and diazocompounds and their reactivity with of Dr. Gilheany, researching novel routes to P-stereogenic compounds. carbonyl groups and olefins. In 2006, she was a visiting postdoctoral fellow Since 2005, he has been the research officer in the group of Prof. Aggarwal for 6 months with Professor Antoine Baceiredo in Toulouse, France, in the University of Bristol. working with phosphorous and sulfur bisylides. In June 2006, she was awarded a Beatriu de Pino´s Fellowship for 2 years in the group of Professor Aggarwal, where she works on the synthesis and applications of new chiral sulfides. Eddie L. Myers graduated with a B.A. (Natural Science) from Trinity College Dublin in 2000. Under the supervision of Dr. Youla Tsantrizos, he received a M.Sc. (Chemistry) from McGill University, Canada, in 2003, working on peptide nucleic acid (PNA) analogs. Under the supervision of Prof. Varinder Michael A. Shaw was born in Glasgow, in the west of Scotland, U.K. Aggarwal, he earned a Ph.D. from University of Bristol in 2007, working − − During his undergraduate degree, he spent a year working with Millennium on the development of novel Morita Baylis Hillman-type reactions. He Pharmaceuticals and an ERASMUS placement at the University of Alicante, is currently pursuing postdoctoral research in the laboratory of Prof. Ronald − Spain. He then graduated with an M.Sci. from the University of Strathclyde Raines at the University of Wisconsin Madison. in 2004. Thereafter, he spent a further year working with Professor John Murphy at Strathclyde on the synthesis of novel chalcogenide-based consist of the elements O, S, Se, and Te. The name is electron-transfer reagents, before moving to the University of Bristol to generally considered to mean “ore former”, from the Greek undertake his Ph.D. research with Professor Varinder Aggarwal. His work chalcos (ore) and -gen (formation). The review is organized there is focused on the ylide-mediated synthesis of enantioenriched aziridines and their application in the asymmetric synthesis of indole according to reaction classes, rather than a discussion of each alkaloids. of the elements in turn, as this tends to be how chemists loadings. The catalysts consist of compounds with two single think. Furthermore, this allows us, where appropriate, to - compare the reactivity/selectivity of different chalcogenides carbon chalcogen bonds only (e.g., a sulfide), where the in a particular reaction. Our own interest in this area started chalcogen atom is vital for the catalytic activity. To the best with the exploration of sulfides as catalysts in ylide-mediated of our knowledge, we have described all instances where a epoxidations. Many of the reactions described herein involve chalcogenide has been used as a catalyst until June 2007. It catalysis of ylide-mediated reactions, and it is with these should be noted that there are many related publications reactions we begin. where a chalcogenide salt is used in substoichiometric amounts in ylide reactions and generates the corresponding chalcogenide in situ. We will provide leading references only 1.1. Scope for these chemistries. Within this review, we have taken the broad definition of a catalyst to be a compound that takes part in the reaction 2. Epoxidation but is regenerated during the course of the reaction. Instances where stoichiometric amounts of catalyst are used are Epoxides are important building blocks and versatile described, but the focus is on the use of substoichiometric substrates in organic synthesis. The synthesis of epoxides Chalcogenides as Organocatalysts Chemical Reviews, 2007, Vol. 107, No. 12 5843 Scheme 1. Comparison of Ways to Synthesize an Epoxide from a Carbonyl Compound Scheme 2. Epoxidation Reaction Using a Sulfur Ylide Samantha L. Riches was born in Exeter in the United Kingdom. She studied chemistry at the University of Bristol, obtaining her M.Sci. in 2004. She then went on to undertake her Ph.D. research under the supervision of Professor Varinder Aggarwal. Her current research focuses on the chemistries in one step. Chalcogenide-catalyzed ylide ep- application of asymmetric sulfur ylide cyclopropanation reactions towards the total synthesis of marine natural products. oxidations shall be described below. 2.1. Sulfide-Catalyzed Epoxidations Stoichiometric sulfur ylide-mediated epoxidations were first reported in 1958 by Johnson and LaCount.1 Since then, and after the establishment of the well-known method of Corey and Chaykovsky,2 many improvements have been made to these reactions.3 The reaction involves the attack of an ylide on a carbonyl group, which yields a betaine intermediate that collapses to give an epoxide and a sulfide (which can be recovered) (Scheme 2). It is important to note that there are two main ways of carrying out the ylide-mediated epoxidation reaction; one involves the preformation and isolation of a sulfonium salt from a sulfide, which then is deprotonated to give an ylide that can then react with the carbonyl group.4-10 The other Varinder K. Aggarwal was born in Kalianpur in North India in 1961 and method, on which we will focus, is the formation of an ylide emigrated to the United Kingdom in 1963. He received his B.A. (1983) from a sulfide followed by reaction with the carbonyl group and Ph.D. (1986) from Cambridge University, the latter under the guidance in the same pot.4,6,10-13 The reaction returns the starting of Dr.
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