Computational studies alkynylation

The selectivity of the hydrogen transfer is excellent When employing a catalyst with deuterium at the a-positions of the isopropoxide ligands (17), complete retention of the deuterium was observed. A computational study using the density functional theory comparing the six-membered transition state (as in Scheme 20.3, the direct transfer mechanism) with the hydride mechanism (Scheme 20.3, the hydride mechanism) supported the experimental results obtained [36]. A similar mechanism has been proposed for the MPV alkynylations [37] and cyanations [38]. 

The CDC between A-f-butyl nitrones and terminal alkynes to form alkynylated nitrones in good to excellent yields, catalysed by zinc trifiate, was achieved using 3,3, 5,5 -tetra-tertbutyldipheno-quinone and O2 as oxidants. The alkynylated nitrones were transformed to regioisomerically pure 3,5-disubstituted isoxazoles. Experimental and DFT computational studies of Pd(OAc)2/pyridine-catalysed intramolecular aerobic oxidative amination of alkenes supported a stepwise mechanism that involved (i) the formation of a Pd(ll)-amidate-alkene chelate with release of 1 equiv. of pyridine and AcOH from the catalyst centre, (ii) insertion of alkene into a Pd—N bond. 

Perhaps, the most common approach for the synthesis of the alkyl-substituent l,3-oxazin-6-ones 475 is the cycHzation of 3-acylaminoacrylic adds and esters, best conducted, under thermal conditions, in accordance with the rule. The reaction proceeds via the intermediate generation of acylimino ketenes 474, which can be subjected to electrocyclization into the 1,3-oxa-zin-6-one derivatives (Scheme 150(a)) (1996T3163, 1977TL1053). Cyclo-addition of acyhsocyanate 469 with the alkynyl ether was observed to give imidoylketene 474, which was in turn converted to compound 475 (1986JCS(P2)961). Results of computational studies indicate interconversion of the A/-formylazetinone 476 into l,3-oxazin-6-ones 475 via two... 

A computational study of gold-catalysed annulations of 3-aryloxy alkynyl indoles has been reported Indole derivatives of electron-donating and electron-withdrawing protective groups undergo the 5-exo-dig cyclization upon activation by cationic [PR3AU-I-] species (Scheme 129). 

The reactions on Rh/Ir usually proceed via oxidative addition to give hydrido (alkynyl) complexes, which then undergo 1,3-H shifts to form the vinylidene complexes. In general, a unimolecular mechanism has been considered to be operative. Recent studies of RhCl(PPr 2R)2 (R = C=NCBu =CHNMe) complexes have shown a remarkable acceleration of the isomerization, with the =C=CHBu complex being formed within seconds [32]. Suitable cross-over experiments showed that a bimolecular mechanism, earlier suggested by some experimental and computational results [33], did not operate. 

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