Cycloadditions organometallic

V.V. Fokin, M. Ahlquist, Enhanced reactivity of dinuclear copper(I) acetylides in dipolar cycloadditions, Organometallics 26 (2007) 4389-4391. 

Doherty, S., Smyth, C.H., Harrington, R.W. and Clegg, W. (2008) Highly enantioselective synthesis of pseudo-Ci-symmetric axially chiral biaryl diphosphines via rhodium-catalyzed double [24-24-2] cycloaddition. Organometallics, 27(19), 4837-4840. 

Although not of industrial importance, many organometallic approaches have been developed (38). A one-pot synthesis of vitamin has been described and is based on the anionic [4 + 2] cycloaddition of three-substituted isoben2ofuranones to l-phytyl-l-(phenylsulfonyl)propene. Owing to the rather mild chemical conditions, the (H)-stereochemistry is retained (39). 

Intramolecular [3-1-2] cycloadditions, i.e., having the TMM moiety and the acceptor linked by a tether, have great synthetic utility in polycarbocycle construction. The construction of 5.5, 6.5, and 7.5 ring systems has been demonstrated with this methodology [21-25]. A number of efficient routes to acyclic precursors were developed (Scheme 2.11). The organometallic reagent (31), generated from 2-bro-mo-3-(trimethylsilyl)propene (32) [26], is a key component in the construction of... 

A subsidiary approach involves nuclear modification of the arylsilanes so obtained. The requisite organometallics can be prepared from aryl halides, or by deprotonation of a suitably activated (c.g. methoxy-substituted) arene. A more specialized route involves cycloaddition between alkynylsilanes and diynes. 

Ade, A., Cerrada, F., Contel, M., Laguna, M., Merino, P. and Tejero, T. (2004) Organometallic gold(III) and gold(I) complexes as catalysts for the 1,3-dipolar cycloaddition to nitrones synthesis of novel gold-nitrone derivatives. Journal of Organometallic Chemistry, 689(10), 1788-1795. 

Organometallic dithiocarbimates are also known. Thus, a diarylgermanium phenyldithiocarbimate, Tbt(Tip)GeS2C=N-Ph, was obtained from the kinetic-ally stabilized diarylgermylene Tbt(Tip)Ge in a reaction with phenyl isothiocyanate, via [2+2] cycloaddition of a diarylgermanethione [Tbt(Tip)Ge=S] intermediate, evidenced by electronic spectroscopy.425... 

A remarkable example of cycloaddition of organometallic dienophiles with 1,1-dimethyl-2,5-diphenylsilacyclopentadiene45 is shown in Scheme 7. 

The use of group 6 heteroatom stabilized carbene complexes (Fischer carbene complexes) in organic synthesis is relatively recent and, in spite of that, it has already produced impressive synthetic results [1]. These versatile organometallic reagents have an extensive chemistry, and they are probably one of the few systems that undergo cycloadditions of almost any kind. For instance, [1+2], [2+2], [3+2], [3+3], [4+1], [4+2], [4+3], [6+3]... 

The present volume contains 13 chapters written by experts from 11 countries, and treats topics that were not covered, or that are complementary to topics covered in Volume 1. They include chapters on mass spectra and NMR, two chapters on photochemistry complementing an earlier chapter on synthetic application of the photochemistry of dienes and polyenes. Two chapters deal with intermolecular cyclization and with cycloadditions, and complement a chapter in Volume 1 on intramolecular cyclization, while the chapter on reactions of dienes in water and hydrogen-bonding environments deals partially with cycloaddition in unusual media and complements the earlier chapter on reactions under pressure. The chapters on nucleophiliic and electrophilic additions complements the earlier chapter on radical addition. The chapter on reduction complements the earlier ones on oxidation. Chapters on organometallic complexes, synthetic applications and rearrangement of dienes and polyenes are additional topics discussed. 

N-Metalated azomethine ylides generated from a-(alkylideneamino) esters can exist as tautomeric forms of the chelated ester enolate (Scheme 11.8). On the basis of the reliable stereochemical and regiochemical selectivities described below, it is clear that the N-metalated tautomeric contributor of these azomethine ylides is important. Simple extension of the above irreversible lithiation method to a-(alkylideneamino) esters is not very effective, and cycloadditions of the resulting lithiated ylides to a,p-unsaturated carbonyl compounds are not always clean reactions. When the a-(alkylideneamino) esters bear a less bulky methyl ester moiety, or when a,P-unsaturated carbonyl compounds are sterically less hindered, these species suffer from nucleophilic attack by the organometallics, or the metalated cycloadducts undergo further condensation reactions (81-85). 

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