Transition metal catalysis intramolecular

Allyloxysilyl)diazoacetic esters 6 and the homologous butenyloxy derivative 9 undergo intramolecular cyclopropanation to form 7 and 10, respectively, when decomposed photochemically or by transition metal catalysis. The thermal reaction of 9 produces the same result, whereas the l-oxa-2-sila-3-cyclopentene 8 is formed from 6, presumably via a pyrazoline intermediate. 

Several examples of transition metal catalysis for the synthesis of piperidines appeared this year. Palladium catalyzed intramolecular urethane cyclization onto an unactivated allylic alcohol was described as the key step in the stereoselective synthesis of the azasugar 1-deoxymannojirimycin . A new synthetic entry into the 2-azabicyclo[3.3.1]nonane framework was accomplished through a palladium mediated intramolecular coupling of amine tethered vinyl halides and ketone enolates in moderate yields . A palladium catalyzed decarboxylative carbonylation of 5-vinyl... 

The Alder-ene reaction has traditionally been performed under thermal conditions—generally at temperatures in excess of 200 °C. Transition metal catalysis not only maintains the attractive atom-economical feature of the Alder-ene reaction, but also allows for regiocontrol and, in many cases, stereoselectivity. A multitude of transition metal complexes has shown the ability to catalyze the intramolecular Alder-ene reaction. Each possesses a unique reactivity that is reflected in the diversity of carbocyclic and heterocyclic products accessible via the transition metal-catalyzed intramolecular Alder-ene reaction. Presumably for these reasons, investigation of the thermal Alder-ene reaction seems to have stopped almost completely. For example, more than 40 papers pertaining to the transition metal-catalyzed intramolecular Alder-ene reaction have been published over the last decade. In the process of writing this review, we encountered only three recent examples of the thermal intramolecular Alder-ene reaction, two of which were applications to the synthesis of biologically relevant compounds (see Section 10.12.6). 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

Intramolecular addition of amine N-H bonds to carbon-carbon multiple bonds would afford nitrogen heterocycles. To realize catalytic cyclization of a,co-aminoalkenes or aminoalkynes, various catalytic systems have been developed especially with early transition metals such as titanium, zirconium, lanthanide metals, and actinide metals [ 12], Late-transition-metal catalysis based on Ni, Pd, and Rh has also proved to be efficient [ 12], Recently, the ruthenium-catalyzed intramolecular hydroamination of aminoalkynes 15 was reported to afford 5-7-membered ring products 16 in various yields (Eq. 6) [13]. Among... 

With the aid of transition-metal catalysis, heterocycle formations can be achieved not only by carbon-heteroatom bond forming cydizations of an acyclic molecule with a terminal group such as alcohols and amines, but also by intramolecular carbon-carbon bond forming reactions of an acyclic precursor containing one or more heteroatoms in its tether moiety. This section will briefly survey heterocycle synthesis via carbon-carbon bond formations. For details of ruthenium-catalyzed C-C bond formations, see other chapters of this book. 

Vinyl stannanes also undergo oxidative homo-coupling under transition metal catalysis to result in dienes (equation An intramolecular version of this method... 

Methods for lactone synthesis by transition metal catalysis involving C—O formation developed over the past 50 years have demonstrated much promise. Indeed, lactones have inspired the discovery of new organometallic transformations, design of metal catalysts, and detailed understanding of reaction mechanisms. Issues of waste minimization and stereoselectivity have been addressed. Future developments for chiral lactone synthesis will likely focus on establishing efficient transformations with broad scope and application in complex molecule total synthesis, especially in regards to macrolactonization where entropic costs often plague intramolecular reactivity with undesired intermolecular reactions. 

We have already mentioned the importance of transition metal catalysis in the field of heterocyclic synthesis, and numerous examples of such applications have been reported throughout the text (see also the References section for further reviews). Generally, the problem of heterocycle formation can be solved by the application of typical transition metal catalyzed processes to intramolecular reactions. 

The rapid development of organocatalysis impels chemists to discover new synthetic methodologies. Many important transformations that could only be realized by transition metal catalysis can now be achieved via organocatalysis. In 2010, Kim and coworkers reported a novel C-H bond functionalization reaction via a tandem 1,5-hydride transfer/ring closure sequence. Based on the iminium-enamine cascade activation of catalyst 33, the fused tetrahydroquino-Unes 35 could be synthesized from substrates 34 with good stereoselectivity. This is the first example of an organocatalytic intramolecular redox reaction (Scheme 36.10) [16]. 

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