Academic literature on the topic 'Cuprate addition'

The Zoanthus alkaloids, exemplified by (-)-norzoanthamine 3a and zoanthamine 3b, show promising activity against osteoporosis. Susumu Kobayashi of the Tokyo University of Science assembled (Angew. Chem. Int. Ed. 2009, 48, 1400; Angew. Chem. Int. Ed. 2009, 48, 1404) the challenging tricyclic core of 3a employing the intramolecular Diels-Alder cyclization of 1 to 2. The cyclopentane of 1 served as useful scaffolding, even though it was cleaved en route to 3a. The cyclohexane ring of 1 has five of its six positions substituted, including three that are alkylated quaternary centers. The starting point for the preparation of 1 was the enantiomerically-pure Hajos-Parrish ketone 4, containing the first of the those quaternary centers. Conjugate addition of MeLi established the second quaternary center. The less stable endo alkyl branch of 1 was installed by conjugate addition to the more reactive α-methylene ketone of the cross-conjugated 5, followed by kinetic quench. Addition of vinyl cuprate across the open face of the enone 7 then established the final quaternary center, setting the stage for the intramolecular Diels-Alder reaction. The silyl enol ether from the cyclization of 1 was not stable, so it was directly oxidized to the enone 2. The keto phosphonate 16 for the last two rings of 3a was prepared from the previously-reported crystalline glutamic acid-derived mesylate 12. Reduction and homologation delivered the ester 14, that was condensed with the phosphonate anion 15 to give 16. The congested cyclopentanone 17, derived from 2, was most efficiently deprotonated with n -BuLi. Exposure of the resulting silyl enol ether to ozone led to the α-hydroxylated product 18. Unexpectedly but happily, oxidative cleavage of 18 delivered, after deprotection and reprotection, the more congested aldehyde 19. This cleavage may be proceeding by tautomerization of 18 to the regioisomeric keto alcohol. The aldehyde 19 was condensed with the keto phosphonate 16, to give, after hydrogenation, the keto lactone 20. A series of oxidation state adjustments then completed the synthesis of (-)-norzoanthamine 3a.

Richard J. K. Taylor of the University of York has developed (Angew. Chem. Int. Ed. 2008, 47, 1935) the diasteroselective intramolecular Michael cyclization of phosphonates such as 2. Quenching of the cyclized product with paraformaldehyde delivered ( + )-Paeonilactone B 3. Roberto Fernández de la Pradilla of the CSIC, Madrid established (Tetrahedron Lett. 2008, 49, 4167) the diastereoselective intramolecular hetero Michael addition of alcohols to enantiomerically-pure acyclic sulfoxides such as 4 to give the allylic sulfoxide 5. Mislow-Evans rearrangement converted 5 into 6, the enantiomerically-pure core of Ethyl Deoxymonate B 7. The ellagitannins, represented by 10, are single atropisomers around the biphenyl linkage. David R. Spring of the University of Cambridge found (Organic Lett. 2008, 10, 2593) that the chiral constraint of the carbohydrate backbone of 9 directed the absolute sense of the oxidative coupling of the mixed cuprate derived from 9, leading to Sanguiin H-5 10 with high diastereomeric control. A key challenge in the synthesis of the solandelactones, exemplified by 14, is the stereocontrolled construction of the unsaturated eight-membered ring lactone. James D. White of Oregon State University found (J. Org. Chem. 2008, 73, 4139) an elegant solution to this problem, by exposure of the cyclic carbonate 11 to the Petasis reagent, to give 12. Subsequent Claisen rearrangement delivered the eight-membered ring lactone, at the same time installing the ring alkene of Solandelactone E 14. AD-mix usually proceeds with only modest enantiocontrol with terminal alkenes. None the less, Ian Paterson, also of the University of Cambridge, observed (Angew. Chem. Int. Ed. 2008, 47, 3016, Angew. Chem. Int. Ed. 2008, 47, 3021) that bis-dihydroxylation of the diene 17 proceeded to give, after acid-mediated cyclization, the bis-spiro ketal core 18 of Spirastrellolide A Methyl Ester 19 with high diastereocontrol.

In this chapter, several of the most important experimental techniques are described. These have been used to probe the most fundamental properties of the superconducting state: the energy gap and the pairing interaction. These methods have played a crucial role in validating the mechanism of superconductivity in conventional superconductors and are key to a fundamental understanding of superconductivity in more recently discovered novel superconductors like cuprates, Fe-based superconductors, and so on. The techniques that are described are all spectroscopic: tunnelling of quasiparticles through an insulating barrier or through a point contact ,Josephson tunnelling, the interaction of photons with a superconducting film or surface, the attenuation of ultrasonic waves,, the relaxation and/or resonance of muons interacting with a superconducting compound, and resonant inelastic X-ray scattering (RIXS). High-pressure techniques and the preparation of thin films and junctions are described. In addition, a state-of-the-art experimental procedure that enables the observation of the Little mechanism is discussed.

Erick M. Carreira of ETH-Zürich generated (Org. Lett. 2012, 14, 2162) ethyl diazoacetate in situ in the presence of the alkene 1 and an iron catalyst to give the cyclopropane 3. Joseph M. Fox of the University of Delaware inserted (Chem. Sci. 2012, 3, 1589) the Rh carbene derived from 5 into the alkene 4 to give the cyclopropene 6, without β-hydride elimination. Masaatsu Adachi and Toshio Nishikawa of Nagoya University reduced (Chem. Lett. 2012, 41, 287) the enone 7 to give the cyclobutanol 8. Intramolecular ketene cycloaddition has been limited to very electron-rich acceptor alkenes. Xiao-Ping Cao and Yong-Qiang Tu of Lanzhou University devised (Chem. Sci. 2012, 3, 1975) a protocol that converted 9 into the cyclobutanone 10 with high diastereocontrol. The intermediate is the tosylhydrazone of the ketone, so a reductive workup would lead to the corresponding cycloalkane. Koichi Mikami of the Tokyo Institute of Technology added (J. Am. Chem. Soc. 2012, 134, 10329) alkyl cuprates to the prochiral enone 11 to give the enolate trapping product 13 in high ee and with high diastereocontrol. Marcus A. Tius of the University of Hawaii found (Angew. Chem. Int. Ed. 2012, 51, 5727) a Pd catalyst for the Nazarov cyclization of 14 to 15. Antoni Riera and Xavier Verdaguer of the Universitat de Barcelona prepared (Org. Lett. 2012, 14, 3534) 16 by enantioselective Pauson-Khand addition to tetramethyl norbornadiene. Conjugate addition followed by retro Diels-Alder could potentially lead to the cyclopentenone 17. The intermolecular Pauson-Khand cyclization often gives mixtures of regioisomers. José Barluenga of the Universidad de Oviedo demonstrated (Angew. Chem. Int. Ed. 2012, 51, 183) an alternative, the addition of an alkenyl lithium 19 to the Fischer carbene 18 leading to 20. Jian-Hua Xie and Qi-Lin Zhou of Nankai University hydrogenated (Adv. Synth. Catal. 2012, 354, 1105; see also Org. Lett. 2012, 14, 2714) the ketone 21 under epimerizing conditions to give the alcohol 22. Kozo Shishido of the University of Tokushima observed (Tetrahedron Lett. 2012, 53, 145) that the intramolecular Heck cyclization of 23 proceeded with high diastereocontrol. Zhi-Xiang Yu of Peking University devised (Org. Lett. 2012, 14, 692) an Rh catalyst for the cyclocarbonylation of 25 to 26.