Author: David González GálvezPublisher:
ISBN:
Category :
Languages : en
Pages : 221
Book Description
Enantioselective Approach to Securinega Alkaloids
Author: David González GálvezPublisher:
ISBN:
Category :
Languages : en
Pages : 221
Book Description
Discovery and Investigation of Trialkylborane/water-mediated Radical Reactions and an Enantioselective Approach to the Securinega Alkaloids
Author: Matthew Richard MedeirosPublisher:
ISBN:
Category :
Languages : en
Pages : 358
Book Description
Studies Toward the Enantioselective Total Synthesis of the Martinella Alkaloids
Author: Vivek BadarinarayanaPublisher:
ISBN: 9780542722608
Category : Chemistry, Organic
Languages : en
Pages :
Book Description
This dissertation consists of two parts. The first part describes the enantioselective total synthesis of martinellic acid. The Martinella alkaloids have attracted considerable attention in the synthetic community over the past few years. This interest is due in large part to their unique structure and useful biological activity (bradykinin receptor antagonist). In model systems we have successfully used the [3+2] azomethine ylide-alkene cycloaddition to construct the heterocyclic core of these alkaloids. The enantioselective approach described herein also involves the azomethine ylide-alkene cycloaddition as a key step in the total synthesis. The pyrrolo[3,2-c]quinoline core of this alkaloid was constructed in an enantioselective fashion by the elaboration of an N-aryl pyrrolidinone, which was obtained via Pd-catalyzed aryl amination reaction using a non-racemic lactam. Pirkle's chiral solvating agent was successfully used to demonstrate the stereochemical integrity of not only the N-aryl lactam (obtained by Pd-catalyzed cross-coupling) but also the cycloaddition precursor and the cycloaddition product (tetracyclic pyrroloquinoline core). The tetracyclic compound obtained via the azomethine ylide-alkene cycloaddition was elaborated to ( - )-martinellic acid in 11 steps and 6% overall yield. The second part of this dissertation describes application of several novel organometallic complexes for carrying out various organic transformations. A fluorinated tris(pyrazolyl)borato silver(I) complex catalyzes the addition of ethyl diazoacetate to benzene rings, providing norcaradienes, which undergo electrocyclization to provide the corresponding cycloheptatriene (the Bu & huml;chner reaction). These reactions are surprisingly selective for addition to the aromatic moiety rather than C-H insertion. A copper complex containing a fluorinated triazapentadienyl ligand has been used to catalyze some carbene and nitrene addition and insertion chemistry. Nitrene addition occurs rapidly and with both aryl and alkyl substituted olefins providing the corresponding aziridine. The carbene transfer reactions that were attempted include C-H insertion, O-H insertion and N-H insertion, of which the latter two were very efficient.
Enantioselective Total Syntheses of Akuammiline Alkaloids and Arynes as Building Blocks for Enantioenriched Products
Author: Elias PicazoPublisher:
ISBN:
Category :
Languages : en
Pages : 564
Book Description
This dissertation features two projects concerning natural product synthesis and reaction development. The importance of natural product synthesis in chemistry and medicine cannot be overstated. In addition to providing a complex setting to test and apply new synthetic methodologies, natural products play a vital role in public health. Their influence in the pharmaceutical industry is profound, as approximately half of all chemical entities to treat disease come from natural product mimics, derivatives, or natural products themselves. With new natural products being discovered daily, there exists an ongoing need to develop efficient syntheses of these compounds and their derivatives. Chapters One, Two, Three, and Four focus on an unusual variant of the Fischer indolization reaction and its application in the total synthesis of a particularly interesting class of indole alkaloids named the akuammilines. Specifically, Chapter One provides an overview of the so-called 'interrupted Fischer indolization reaction'. This reaction is described from a methodological standpoint and is then evaluated in the context of akuammiline alkaloid total synthesis. Chapters Two, Three, and Four describe enantioselective syntheses of various akuammiline alkaloids, in addition to several akuammiline alkaloid derivatives. Central to our approach was the development of modern variants of the classic Fischer indolization reaction to generate high levels of complexity. These efforts culminated in the first enantioselective total syntheses of (-)-aspidophylline A, (+)-strictamine, (-)-2(S)-cathafoline, (-)-pseudoakuammigine, (+)-akuammiline, (-)-10-demethoxyvincorine, and derivatives therein. Chapters Five describes an application of the distortion/interaction model to a variety of mono and disubstituted benzynes and substituted indolynes. Chapter Six is focused on the development of a facile method to synthesize stereodefined quaternary centers from reactions of arynes and related strained intermediates with b-ketoester-derived substrates. Our approach provides a general solution to the challenging problem of stereoselective b-ketoester arylation/alkenylation, with formation of a quaternary center with enantiomeric excess up to 96%.
Transaminase Triggered Aza-Michael Approach for the Enantioselective Synthesis of Chiral Alkaloids
Author: James RyanTowards the Enantioselective Synthesis of Lycoricidine Alkaloids
Author: Ruowei MoPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Two efficient, regio- and stereo controlled synthetic approaches to the synthesis of racemic analogs of pancratistatin have been accomplished and they serve as the model systems for the total synthesis of optically active 7-deoxy-pancratistatin. In the Diels-Alder approach, an efficient [4+2] cycloaddition of 3,4-methylenedioxyco- nitrostyrene with Danishefsky's diene to selectively form an exo-nitro adduct has been developed as the key step in the construction of the C-ring of the target molecule. In the Michael addition approach, the key step was a conjugate addition of an organic zinc-cuprate to the 3,4-methylenedioxy-(B-nitrostyrene, followed by a diastereocontroUed closure to form the cyclohexane C-ring of the target molecule via an intramolecular nitro-aldol cyclization on a neutral alumina surface. A chair-like transition state for such a cyclization has been established and such a chelation controlled transition state can be useful in the prediction of diastereoselectivity in other related 6-exo-trig nitroaldol reactions. Cyclization of the above products fi^om both approaches by using a Bischler-Napieralski type reaction afforded two lycoricidine derivatives 38 and 50 in good yields. The initial results from the above modeling studies as well as the analysis of the synthetic strategy were directed to a chiral pool approach to the total synthesis of optically active 7-deoxy-pancratistatin. Selective monsilylation and iodination of Ltartaric acid provided a chiral precursor for the proposed key Michael transformation. The outlook for the total synthesis of 7-deoxy-pancratistatin by this approach is very promising.A concise synthesis of novel designed, optically pure, Cz-symmetrical disulfonylamide chiral ligands starting from L-tartaric acid has also been achieved. This sequence employs the metallation of indole followed by Sfj2 replacement of a dimesylate as the key step. The activity for this Cz-symmetric chiral disulfonamide ligand in the catalytic enantioselective reaction has been confirmed by nucleophilic addition to benzaldehyde in the disulfonamide-Ti (0-i-Pr)4-diethylzinc system with a 48% yield and a 33% e.e. value. Such a ligand tethered with a suitable metal complex should be also applicable towards the total synthesis of 7-deoxy-pancratistatin.
Progress Towards Enantioselective Total Synthesis of the Bisbenzyltetrahydroisoquinoline Alkaloid ( - )- Cycleanine and a New Approach to the Syntheses of Some Isoquinolones
Author: Jianwen CuiPublisher:
ISBN:
Category : Tetrahydroisoquinolines
Languages : en
Pages : 0
Book Description
Enantioselective Syntheses of Indolizidine Alkaloids and Synthetic Studies of Taxol
Author: Jong-Ryoo ChoiPublisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 444
Book Description
Design of Bio-inspired Materials and Total Synthesis of "Securinega" Alkaloids
Author: Robin WehlauchCatalytic Methods in Asymmetric Synthesis
Author: Michelangelo GruttadauriaPublisher: John Wiley & Sons
ISBN: 1118087984
Category : Science
Languages : en
Pages : 721
Book Description
This book covers advances in the methods of catalytic asymmetric synthesis and their applications. Coverage moves from new materials and technologies to homogeneous metal-free catalysts and homogeneous metal catalysts. The applications of several methodologies for the synthesis of biologically active molecules are discussed. Part I addresses recent advances in new materials and technologies such as supported catalysts, supports, self-supported catalysts, chiral ionic liquids, supercritical fluids, flow reactors and microwaves related to asymmetric catalysis. Part II covers advances and milestones in organocatalytic, enzymatic and metal-based mediated asymmetric synthesis, including applications for the synthesis of biologically active molecules. Written by leading international experts, this book consists of 16 chapters with 2000 References and illustrations of 560 schemes and figures.