Propargyl systems

In acyclic propargylic systems, organocopper and -cuprate reagents react similarly to afford allenes. An overall anti-Sfl process is involved, probably via a copper(III) intermediate. Typical examples are shown in Table 3. 

Allylic rearrangements have also been demonstrated in propargyl systems, for example,... 

Triple bonds in the P position (in propargyl systems) have about the same effect as double bonds. Alkyl, aryl, halo, and cyano groups, among others, in the 3 position of allylic substrates increase Sn2 rates, owing to increased resonance in the transition state, but alkyl and halo groups in the 1 position decrease the rates because of steric hindrance. 

This reaction type has been intensely studied °. The application of highly polar solvents, catalysis with tertiary amines" or with acids mesomeric stabilization of intermediate carbenium ions " (allylic and benzylic systems propargylic systems" ) as well as derivatives of sulfinic acids with increasing acidity - usually indicate an ionic pathway (intra- and/or inter-molecular) ... 

The high reactivity of the cobalt-complexed propargylic systems has also allowed for ether oxygens to serve as nucleophiles, which has led to the fashioning of medium-sized ring ethers via ring expansion (Equation (60)), and also... 

The high-valent metal species required for activation of an alkyne has also been generated by the oxidative addition to an allylic or propargylic system. For example, with an allyl aryl ether as the substrate, this type of reaction achieves a cycloisomerization that occurs through an 0- to C-allyl migration (Equation (92)) 323,324 similarly, (9-propargyl derivatives lead to a mixture of allenyl and propargyl products (Equation (93)).325,326... 

The proximity of carbon-carbon double or triple bonds, as in allylic and propargylic systems has little impact upon a fluorine substituent s chemical shift (Scheme 3.69). Note that one would not intuitively expect allyl fluoride and n-butyl fluoride to have such similar chemical shifts. 

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... 

The tandem silylformylation-allylsilylation of a diallylsilyl ether has been reported by Leighton, using [Rh(acac)(CO)2] as the catalyst (equation 11). This method was optimized and extended to propargylic systems where good diastere-oselectivity can be achieved using the isopropyl derivative. A mechanism is proposed for the stereoselectivity involving coordination of the silicon by both of the oxygen atoms (equation 12). 

Such reactivity is likewise known for propargylic systems leading to allenic systems (equation 2). ... 

While in propargylic systems a vinylogous reduction is the normal reactivity, in allylic systems a double bond shift on reduction is realized more generally only when terminal alkenes are produced. Especially Interesting in this respect is the Pd-catalyzed hydrogenolysis of allylic acetates (X = OAc) with ammonium formate (equation 45). ... 

J 1 -HYDROGEN-HYDROGEN TRANSPOSITIONS ISOMERIZATION OF ALLYL AND PROPARGYL SYSTEMS... 

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). 

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