Transition metal propargyl complexes

Dipolar cycloaddition reactions are most commonly applied for the synthesis of five-membered heterocyclic compounds.86 87 [3+2] cycloaddition reactions of transition-metal propargyl complexes have been reviewed.88 Addition of diazomethane to carbene complexes (CO)5Cr= C(OEt)R results in cleavage of the M = C bond with formation of enol ethers H2C = C(OEt)R,3 89 but (l-alkynyl)carbene complexes undergo 1,3-dipolar cycloaddition reactions at the M = C as well as at the C=C bond. Compound lb (M = W, R = Ph) affords a mixture of pyrazole derivatives 61 and 62 with 1 eq diazomethane,90 but compound 62 is obtained as sole... 

Virtually all of the transition metal-propargyl complexes investigated react readily with either neat SO2 or SO2 in organic solvents according to Eq. (24), where M = CpFe(CO)2 (111, 124), CpMo(CO)3 (111, 124),... 

Only recently have early transition metal propargylic complexes been recognized. The lanthanide alkyls [LnCH(SiMe4)2(i7 -C5Me5)2j (Ln = La. Ce) react with the 2-alkynes MeC=CR (R = Me, Et, "Pr) to afford 1,2-disubstituted 3-alkylidenecyclobutenes. The first step in this catalytic cy-... 

Early investigations into the chemistry of tr-bound transition metal propargyl complexes concentrated on their reactivity toward charged and uncharged electrophiles. In the former case r/ -bound allene complexes [ML (r --CH2=C=CH2)]" were formed via protonation [Eq. (21)]... 

C2.12 Transition metal propargyl complexes versatile reagents in synthesis... 

Since the first discovery of transition metal allenylidene complexes (M=G=C=C<) in 1976, " these complexes have attracted a great deal of attention as a new type of organometallic intermediates. Among a variety of such complexes, cationic ruthenium allenylidene complexes Ru =C=C=GR R, readily available by dehydration of propargylic alcohols coordinated to an unsaturated metal center, can be regarded as stabilized propargylic cation equivalents because of the extensive contribution of the ruthenium-alkynyl resonance form... 

Varghese V, Saha M, Nicholas KM (1988) Org Synth 67 141 Nicholas KM (1987) Acc Chem Res 20 207 Caffyn AJM, Nicholas KM (1995) Transition metal alkyne complexes transition metal stabilized propargyl system. In Abel EW, Stone FGA, Wilkinson G (eds) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford, p 685 Schreiber SL, Klimas MT, Sammakia T (1987) J Am Chem Soc 109 5749 Nakamura T, Matsui T, Ta-nino K, Kuwajima I (1997) J Org Chem 62 3032... 

Nicholas, K. M., Caffyn, A. J. M. Transition metal alkyne complexes Transition metal-stabilized propargyl systems, in Comprehensive Organometallic Chemistry II. (eds. Abel, E. W., Stone, F. G. A.,Wilkinson, F.), 12, 685-702 (Oxford, 1995). 

Allenylidenes ligands are divalent radicals derived from allenes and their metal derivatives can be easily obtained from terminal propargylic alcohols by dehydration of initially formed M-hydroxyvinylidenes [174]. Since the first report of the use of transition metal allenylidene complexes in catalytic reactions by Trost [94], significant progress in this field has been made [59, 64, 65, 175]. The reactivities of metal allenylidene complexes are rationalized by considering the electrophilicity of Ca and Cy and the nucleophilicity of Cp of the M=C=C=CR2 moiety. 

Various transition metal complexes, in particular of late transition metals, were reported to be effective catalysts for such double bond isomerization. Because organic synthesis is the focus of this volume, this section will cover the transition metal-catalyzed isomerization of alkenes, which has the significant synthetic and industrial utilities. This chapter will also include the synthetic application, asymmetric reactions,4-6 and isomerization of alkynes, in particular, that of propargylic alcohols. 

The best enantioselectivity (35% ee) was observed in the reaction of l-(l-naphthyl)-2-propyn-l-ol with acetone in the presence of a complex bearing a 1-naphthylethylthio-lato moiety as a chiral ligand. Although the enantioselectivity is not yet satisfactory, this was the first example of an enantioselective propargylic substitution reaction catalyzed by transition metal complexes [27]. It is noteworthy that the chiral thiolate-bridged ligands work to control the chiral environment around the diruthenium site. 

The transition metal catalysed formation of five membered heterocycles through the insertion of a triple bond has also been explored. o-Halophenyl-alkynylamines, propargylamines and propargyl-ethers have been subjected to ring closure reactions. These processes, however also require the presence of a second, anionic reagent, which converts the palladium complex formed in the insertion step to the product. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

REACTIONS OF SULFUR DIOXIDE WITH o-ALLYL, PROPARGYL, CYCLOPROPYL, AND CYCLOPROPYLMETHYL COMPLEXES OF TRANSITION METALS... 

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