Enantioselective Total Synthesis of Guanacastepenes A and E PDF Download
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Author: William D. Shipe
Publisher:
ISBN:
Category : Cyclobutane
Languages : en
Pages : 340
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Book Description
The evolution of a convergent strategy that led to efficient, enantioselective syntheses of guanacastepene E and guanacastepene A (formal) is described. The first chapter of this thesis provides background information on (1) the isolation and biology of the guanacastepene family of secondary metabolites, (2) the substantial synthetic work carried out by other research groups toward their synthesis, and (3) the basis of our ultimate approach to the natural product. The synthesis of a fully functionalized C ring and two major model studies that provided critical information about the system are described in the second chapter. The final chapter describes (1) the enantiospecific synthesis of an A ring fragment from R-(-)-carvone, including a novel ring-contracting reaction, (2) the classical resolution of the C ring, and (3) the union of the two enantiopure fragments and further elaboration, culminating in the enantioselective total synthesis of both the natural (+)- and unnatural (-)-guanacastepene E and a formal total synthesis of (+)-guanacastepene A. The foundation of our convergent approach is the following sequence of three reactions: (1) the union of two functionalized building blocks through a [pi]-allyl Stille cross-coupling reaction, (2) the stereoselective construction of the C-11 quaternary carbon center with a [2+2] photocycloaddition, and (3) the stereoselective, reductive fragmentation of a cyclobutyl bond to form the seven-membered central B ring of the guanacastepenes.
Author: William D. Shipe
Publisher:
ISBN:
Category : Cyclobutane
Languages : en
Pages : 340
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Book Description
The evolution of a convergent strategy that led to efficient, enantioselective syntheses of guanacastepene E and guanacastepene A (formal) is described. The first chapter of this thesis provides background information on (1) the isolation and biology of the guanacastepene family of secondary metabolites, (2) the substantial synthetic work carried out by other research groups toward their synthesis, and (3) the basis of our ultimate approach to the natural product. The synthesis of a fully functionalized C ring and two major model studies that provided critical information about the system are described in the second chapter. The final chapter describes (1) the enantiospecific synthesis of an A ring fragment from R-(-)-carvone, including a novel ring-contracting reaction, (2) the classical resolution of the C ring, and (3) the union of the two enantiopure fragments and further elaboration, culminating in the enantioselective total synthesis of both the natural (+)- and unnatural (-)-guanacastepene E and a formal total synthesis of (+)-guanacastepene A. The foundation of our convergent approach is the following sequence of three reactions: (1) the union of two functionalized building blocks through a [pi]-allyl Stille cross-coupling reaction, (2) the stereoselective construction of the C-11 quaternary carbon center with a [2+2] photocycloaddition, and (3) the stereoselective, reductive fragmentation of a cyclobutyl bond to form the seven-membered central B ring of the guanacastepenes.
![Synthesis of the Tricyclic Core of Guanacastepene A, Decarboxylative Rearrangement of Allenylic N-tosyl Carbamates and Phosphine-catalyzed Intramolecular [gamma]-umpolung Addition of [alpha]-aminoalkylallenic Esters, and the Enantioselective Total Synthesis of (+)-ibophyllidine PDF](https://books.google.com/books/content/images/frontcover/xERQnQAACAAJ?fife=w80-h100)
Author: Ian Paul Andrews
Publisher:
ISBN:
Category :
Languages : en
Pages : 233
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Book Description
Chapter 1 The synthesis of the tricyclic core of the diterpene guanacastepene A is described. Based on previous studies in the laboratory of professor Ohyun Kwon, the densely functionalized six-membered ring of the natural product was constructed utilizing an intermolecular Diels-Alder cycloaddition between maleic anhydride and a highly substituted alkoxydiene. The requisite diene was synthesized via a Stille cross coupling reaction for which an efficient synthesis of the necessary vinyl stannane was developed. An alternative synthesis of the diene based on copper mediated coupling of vinyl boronates with alcohols was also devised, which allowed for the preparation of gram quantities with minimal purification. The five-membered ring of guanacastepene A was appended through coupling with a highly functionalized zinc cuprate. While previous studies in the Kwon laboratory showed that a conjugate addition/Mukaiyama aldol strategy to install the C11 methyl group and forge the seven-membered ring was efficient in forming the two desired carbon-carbon bonds, poor diastereoselectivity of the initial conjugate addition was observed. The research described here uses the Nozaki-Hiyama-Kishi reaction to close the central seven-membered ring without prior installation of the C11 methyl group. Chapter 2 The synthesis of 3-carbethoxy-2-substituted-3-pyrrolines via the phosphine-catalyzed intramolecular gamma-umpolung addition of N-tosyl alpha-aminoalkylallenic esters is described. The current transformation provides a compliment to the known syntheses of similarly substituted pyrrolines via the phosphine-catalyzed [3 + 2] annulation between imines and allenoates. The flexibility in substitution at the 2-position, including alkyl groups, offers benefits over many of the previously reported syntheses of similarly substituted pyrrolines. The N-tosyl aplpha-aminoalkylallenic esters were prepared via a novel decarboxylative rearrangement of allenylic carbamates. Chapter 3 The enantioselective total synthesis of the monoterpene indole alkaloid (+)-ibophyllidine is described. The employed strategy was based on a key asymmetric phosphine-catalyzed [3 + 2] annulations between a gamma-ethyl allenoate and the N-tosyl imine derived from indole-3-aldehyde using Kwon's L-4-hydroxyproline-derived chiral phosphine catalyst. This key transformation constructed the stereochemically dense D-ring with exceptional levels of diastereo- and enantioselectivity. A subsequent diastereoselective hydrogenation of the pyrroline double bond led to the fully functionalized, all syn pyrrolidine ring of the natural product. An intramolecular alkylation at the C3 position of indole formed the C-ring while an intramolecular aza Baylis-Hillman reaction was utilized to forge the E-ring leading to the pentacyclic skeleton of (+)-ibophyllidine.
Author: Elias J. Corey
Publisher: Elsevier
ISBN: 0128001518
Category : Science
Languages : en
Pages : 334
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Book Description
Written by world-renowned and best-selling experts, Nobel Laureate E. J. Corey and Laszlo Kurti, Enantioselective Chemical Synthesis offers an authoritative and comprehensive overview of the field's progress; the processes and tools for key formations; future development for complex, stereocontrolled (enantiomeric or diastereoisomeric) molecules; and valuable examples of multi-step syntheses. Utilizing a color-coded scheme to illustrate chemical transformations, Enantioselective Chemical Synthesis provides clear explanation and guidance through vital asymmetrical syntheses and insight into the next steps for the field. Researchers, professionals, and academics will benefit from this valuable, thorough, and unique resource. - In Part I, the authors present clearly, comprehensively and concisely the most useful enantioselective processes available to synthetic chemists. - Part II provides an extensive discussion of the most logical ways to apply these new enantioselective methods to the planning of syntheses of stereochemically complex molecules. This hitherto neglected area is essential for the advancement of enantioselective synthesis to a more rational and powerful level. - Part III describes in detail many reaction sequences which have been used successfully for the construction of a wide variety of complex target molecules - Clearly explains stereochemical synthesis in theory and practice - Provides a handy tool box for scientists wishing to understand and apply chiral chemical synthesis - Describes almost 50 real life examples of asymmetric synthesis in practice and examines how the chiral centers were introduced at key synthetic stages
Author: Paul Allan Renhowe
Publisher:
ISBN:
Category :
Languages : en
Pages : 296
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Author: Sasadhar Majhi
Publisher: World Scientific
ISBN: 9811268703
Category : Science
Languages : en
Pages : 469
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Book Description
Modern Sustainable Techniques in Total Synthesis of Bioactive Natural Products comprises five parts for green tools, such as ultrasonic waves, microwave heating, visible-light photochemistry, organic electrochemistry, and flow chemistry, along with 72 chapters for each bioactive molecule of natural origin. Each chapter explores the natural source, structure, systematic name, structural features, compound class, biological activity, conventional approaches for their chemical synthesis, and demerit(s) of conventional approaches (where applicable). Finally, critical features of total synthesis using modern sustainable techniques, including reaction types, synthetic strategy, and synthetic route utilizing modern sustainable tools for each bioactive natural product and secondary metabolites, are discussed brilliantly. The spectrum of application of total synthesis of bioactive natural products using modern sustainable techniques may promote the development of more eco-friendly synthetic processes so that the next generations can live on this planet with a minimum energy requirement for chemical reactions with the least pollution.
Author: Matthew David Kowalski
Publisher:
ISBN:
Category :
Languages : en
Pages : 404
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Author: Cheryl Faye Lichti
Publisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 186
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Author: Ryan E. Stites
Publisher:
ISBN:
Category :
Languages : en
Pages : 162
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Author: Todd M. Heidelbaugh
Publisher:
ISBN:
Category :
Languages : en
Pages : 694
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Author: Anne Therese Stevens
Publisher:
ISBN:
Category :
Languages : en
Pages : 366
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