Cobalt-mediated propargylation

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,... 

The facile acid-promoted dehydration of cobalt-complexed propargyl alcohols [18], via P-pro-ton loss from the derived cations (Scheme 4-50) offers improved chemo-, regio- and stereoselectivity vis a vis the free propargylic alcohols, with a strong preference for the more substituted ( )-ene-yne complex [151,152]. Such Co-mediated dehydration has afforded routes to enantiomerically pure manicone and normanicone (4,6-dimethyl-4-octen-3-one,... 

Reaction (62) reports the cyclization of a thermally instable propargyl bromide cobalt complex mediated by Ph2SiH2 at room temperature and Et3B/02 as the... 

An additional advantage of the intramolecular protocol stems from the opportunity to prepare easily the required polyfunctional precursors via cobalt carbonyl stabilized propargyl cations. The approach based on the tandem utilization of Co-mediated alkylation and Pauson-Khand annulation was developed in Schreiber s studies to elaborate short pathways for the synthesis of polycyclic compounds. An example of the efficiency of this protocol is the two-step transformation of the acyclic precursor 409 into the tricyclic derivative 410. The cobalt-complexed acetal 409 was first transformed into the cyclooctyne derivative 411 via intramolecular reaction of the in situ generated propargyl cation 409a with the allylsilane moiety. Cyclooctyne 411 underwent smooth cycloaddition in the presence of carbon monoxide to give the target compound 410 with excellent stereoselectivity. 

Propargyl)Co2(CO)g radicals presumably are also involved in the Mn(III)-mediated addition of P-dicarbonyl compounds to complexed 1,3-enynes, which produces highly functionalized dihydrofiuan derivatives 122 (Scheme 4-65) [222, 223]. The chemo-, regio-, and stereoselectivity of these reactions stands in contrast to the variable selectivity associated with the corresponding reactions of free enynes [224]. The formation of ethers 123 in methanol (Scheme 4-65) suggests that the cobalt-propargyl radicals initially produced are rapidly oxidized by Mn(III) to the stabilized carbocations. 

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