Part I. Palladium-catalyzed Silylstannylations of Diynes PDF Download
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Author: Sandeep D. Apte Publisher: ISBN: Category : Chirality Languages : en Pages : 127
Book Description
Abstract: The formation of silylstannyl dienes from 1,6-diynes was first reported by our former research group members. These dienes are fascinating molecules as they exhibit helical chirality. However, monocyclic dienes are known to undergo fast helical isomerization. For our main goal of making a unidirectional helical polyolefin, a diene in which this helical isomerization is completely frozen is necessary. A bicylic motif was designed to obtain such a system by slowing down this isomerization. The chemistry of these silylstannyl dienes was unexplored. We probed the Stille coupling reactions of these compounds with various electrophiles. A new protocol for the Stille coupling which used 2 mol% Pd(MeCN)2Cl2, 4 mol% AsPh3 and 8 mol% CuI in DMF at room temperature was found to be effective for several difficult substrates. Using these conditions, iodobenzene, bromotrimethylsilyl acetylene, benzyl bromide and 1,4-diiodobenzene were efficiently coupled. Synthesis of a polyolefin was attempted by coupling of a silylstannyl diene with its iodide derivative under the same conditions. However, instead of the expected tetraene, a rearranged product was observed which presumably was formed via a 1,7 -hydrogen shift. The Palladium-catalyzed addition of silylstannane reagents to alkynes is known to be a synthetically useful reaction. The tolerance of a sensitive functionality like epoxide iii had not been reported before. We examined the addition of Bu3SnSiMe3 to epoxyalkynes and found that the desired addition product was formed in excellent yields. Such products can be subjected to the well-known Ti(III)-mediated epoxide opening-radical cyclization. The reaction presumably occurs via radical formation followed by an addition-elimination sequence to give the expected product. This reaction affords five-membered carbo- and heterocyclic compounds. The presence of the vinyl-TMS group at the terminal provides a potentially useful alcohol. Similarly epoxyalkynes undergo Pd-catalyzed distannation followed by Ti(III) mediated reaction to give cyclic alcohols with vinylstannane, which is more reactive than the corresponding vinyl vinylsilane. The application of this addition-elimination reaction was expected for the formation of four-membered carbocyclic compounds. However, the radical formed by epoxide opening abstracts the vinyl hydrogen via a 6-membered transition state and an internal alkyne was obtained.
Author: Sandeep D. Apte Publisher: ISBN: Category : Chirality Languages : en Pages : 127
Book Description
Abstract: The formation of silylstannyl dienes from 1,6-diynes was first reported by our former research group members. These dienes are fascinating molecules as they exhibit helical chirality. However, monocyclic dienes are known to undergo fast helical isomerization. For our main goal of making a unidirectional helical polyolefin, a diene in which this helical isomerization is completely frozen is necessary. A bicylic motif was designed to obtain such a system by slowing down this isomerization. The chemistry of these silylstannyl dienes was unexplored. We probed the Stille coupling reactions of these compounds with various electrophiles. A new protocol for the Stille coupling which used 2 mol% Pd(MeCN)2Cl2, 4 mol% AsPh3 and 8 mol% CuI in DMF at room temperature was found to be effective for several difficult substrates. Using these conditions, iodobenzene, bromotrimethylsilyl acetylene, benzyl bromide and 1,4-diiodobenzene were efficiently coupled. Synthesis of a polyolefin was attempted by coupling of a silylstannyl diene with its iodide derivative under the same conditions. However, instead of the expected tetraene, a rearranged product was observed which presumably was formed via a 1,7 -hydrogen shift. The Palladium-catalyzed addition of silylstannane reagents to alkynes is known to be a synthetically useful reaction. The tolerance of a sensitive functionality like epoxide iii had not been reported before. We examined the addition of Bu3SnSiMe3 to epoxyalkynes and found that the desired addition product was formed in excellent yields. Such products can be subjected to the well-known Ti(III)-mediated epoxide opening-radical cyclization. The reaction presumably occurs via radical formation followed by an addition-elimination sequence to give the expected product. This reaction affords five-membered carbo- and heterocyclic compounds. The presence of the vinyl-TMS group at the terminal provides a potentially useful alcohol. Similarly epoxyalkynes undergo Pd-catalyzed distannation followed by Ti(III) mediated reaction to give cyclic alcohols with vinylstannane, which is more reactive than the corresponding vinyl vinylsilane. The application of this addition-elimination reaction was expected for the formation of four-membered carbocyclic compounds. However, the radical formed by epoxide opening abstracts the vinyl hydrogen via a 6-membered transition state and an internal alkyne was obtained.
Author: Sandra Warren Publisher: ISBN: Category : Chirality Languages : en Pages : 886
Book Description
The silylstannane-mediated cyclization of mono-substituted 1,6-diynes is readily catalyzed by palladium in the presence of a weakly coordinating phosphine. The products of the reaction are highly functionalized carbo- or heterocycles. The reaction displays wide functional group compatibility, tolerating groups like carboxylic esters, amines and amides. The reactionis not sensitive to moisture or air, and the isolation of the products is operationally simple. The 1,2-bis-alkylidenecycloalkane products display very interesting stereochemical fearf and stannyl groups are pointing toward each other, despite the apparent steric hindrance thus generated. Second, this stereochemistry of the individual double-bonds can lead to axial chirality in the diene system. It has been shown that the 1,2-bis-alkylidenecycloalkanes are indeed axially chiral at lowtemperatures, but they display a fluxional behavior at room temperature. The coalescence temperatures have been determined for several compounds, ranging from 670ðC to + 20ðC, giving insight into the exchange process and the influence of various substituents. Also, the energies of activation of the exchange process have been determined via NMR Line Shape Analysis for a selected set of compounds. These energies appear to depend not only on the groups on the silicon and the tin, but also on the cyclopentane ring substituents. Free energies of activations in the range of 52.3 to 56.9 kJ.mol-1 were observed. The synthetic applications of these compounds have been the object of preliminary studies. Although many reactions did not yield the desired products, tin-lithium and tin-halogen exchange and epoxidation of the alkenes seem to offer some promise. Diels-Alder reactions of the destannylated products can be carried out in quantitative yield. The first example of a Stille coupling with a vinyl iodide is also described.
Author: Jong Uk Rhee Publisher: ISBN: Category : Catalysis Languages : en Pages :
Book Description
Abstract: Part One: The Barton-McCombie reaction has been widely acknowledged for the efficient deoxygenation of 2° alcohols through radical process. For the chain process, the radical source initially generated by the catalytic amount of AIBN attacks the thiocarbnyl sulfur to produce a radical intermediate that is cleaved at the beta-position to give alkyl radicals. Although the sp3 carbon centered radicals have been used commonly as precursors of 6-exo-trig ring closure, the radical intermediate in the thiourethane-mediated deoxygenation of alcohol has never been considered as a precursor of radical cyclization. However, the radical intermediate can participate in an exo-hex-5-enyl or exo-hept-6-enyl type intramolecular cyclization when a suitable radical acceptor is appropriately placed. Moreover, structurally rare examples of N-furanosides and N-pyranosides have been synthesized efficiently from carbohydrate-derived imidazoyl and triazoyl thioates by utilizing the new Barton's radical-mediated methodology. Depending on the radical acceptors, glycosides with either C2-carbon or C2-amino substituents are formed. The C2 stereogenic center of the N-pyranosides formed via exo-hept-6-enyl type radical cyclization can also be controlled by the stereochemistry of the radical acceptor. While (E)-olefin acceptors make allo/altro mixture, (Z)-olefin acceptors give stereoselectively altro-isomers. Part Two: Palladium catalyzed tandem bifunctionalization/cyclization of enynes, diynes, bis(allenes), alleneynes, allene aldehydes, and allene ketones with R3Sn-SiR'3 is a useful tactic for the synthesis of synthetically interesting heterocyclic and/or carbocyclic compounds. Although the reaction has a broad tolerance to functional groups, operationally simple procedure, and high catalytic turnover and regioselcetivity, the applications of the silylstannylated carbocyclization to further transformation are rare. The palladium catalyzed silylstannylation/cyclization of 1, 6-diynes gives two atropisomeric isomers with axial chirality. The silylstannyl dienes themselves do not take part in Diels-Alder reactions, but the removal of Sn has been achieved efficiently under acidic condition and the resulting silyldienes have restored this reactivity. In this study a number of fused carbocyclic or heterocyclic compounds were made by the Diels-Alder reaction and the regioselectivity was controlled by steric effects. This regioselective Diels-Alder route has been used for the synthesis of an intermediate for a Papulacandin D core synthesis. Asymmetric version of silylstannylation/carbocyclization of alleneynes has been screened with a various chiral phosphine ligands.
Author: Publisher: Elsevier Science ISBN: 9780080445908 Category : Science Languages : en Pages : 778
Book Description
Comprehensive Organometallic Chemistry, (COMC-III), Third Edition, 13 Volume Set is aimed at the specialist and non-specialist alike. It covers the major developments in the field in a carefully presented way with extensive cross-references. COMC-III provides a clear and comprehensive overview of developments since 1993 and attempts to predict trends in the field over the next ten years. Applications of organometallic chemistry continue to expand and this has been reflected by the significant increase in the number of volumes devoted to applications in COMC-III. Organic chemists have edited the volumes on organometallic chemistry towards organic synthesis - this is now organized by reaction type so as to be readily accessible to the organic community. Like its predecessors, COMC (1982) and COMC-II (1995), this new work is the essential reference text for any chemist or technologist who needs to use or apply organometallic compounds. Also available online via ScienceDirect (2006) - featuring extensive browsing, searching, and internal cross-referencing between articles in the work, plus dynamic linking to journal articles and abstract databases, making navigation flexible and easy. For more information, pricing options and availability visit www.info.sciencedirect.com. Presents a comprehensive overview of the major developments in the field since 1993 providing general and significant insights Highlights the expansion of applications in organometallic chemistry with a strong organic synthesis focus Provides a structured first point of entry to the key literature and background material for those planning research, teaching and writing about the area
Author: American Chemical Society. Committee on Professional Training Publisher: ISBN: Category : Biochemistry Languages : en Pages : 1932
Book Description
Faculties, publications and doctoral theses in departments or divisions of chemistry, chemical engineering, biochemistry and pharmaceutical and/or medicinal chemistry at universities in the United States and Canada.
Author: Timothy J. Donohoe Publisher: Georg Thieme Verlag ISBN: 3132452858 Category : Science Languages : en Pages : 570
Book Description
The Science of Synthesis Editorial Board, together with the volume editors and authors, is constantly reviewing the whole field of synthetic organic chemistry as presented in Science of Synthesis and evaluating significant developments in synthetic methodology. Several annual volumes updating content across all categories ensure that you always have access to state-of-the-art synthetic methodology.
Author: Sandeep D. Apte
Author: Sandeep D. Apte
Author: Sandra Warren
Author: 
Author: DENNIS. OSTROVSKY
Author: 
Author: Jong Uk Rhee
Author: 
Author: American Chemical Society. Committee on Professional Training
Author: Timothy J. Donohoe
Author: Robert L. Augustine