By Nakamura I., Yamamoto Y.

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172 The reaction proceeds through the copper-catalyzed isomerization of alkyne to the corresponding allenes 333, followed by the thermal or Cu-mediated 1,2migration of the thio group 334. 173 The reaction is initiated by acetoxypalladation of the alkyne moiety of 335, forming the vinylpalladium intermediate 337. The following cyclization and protonolysis give 336. In the reaction of the alkynylnitriles 338, migration of the acetyl group from the oxygen atom to nitrogen atom occurs in 340 to give the heterocycles 339 (Scheme 107).

The reaction is Transition-Metal-Catalyzed Heterocyclic Synthesis Chemical Reviews, 2004, Vol. 104, No. 5 2169 Scheme 139 Scheme 140 Scheme 141 initiated by oxidative cyclization of 439 with ruthenium, forming the ruthenacycle 442. In the absence of water, isomerization of the R-C-ruthenium ketone 442 to the O-enolate 443 occurs and subsequent reductive elimination gives the pyran 440. Hydration of the ruthenacycle 442 takes place in the presence of water to form the alkenylruthenium hydoxide 444.

226 The intramolecular asymmetric Heck reaction has featured in the synthesis of complex heterocyclic compounds. Bidentate ligands, such as diphosphines (especially BINAP) and phosphine-oxazolines, have been used as a chiral ligand of the asymmetric Heck reaction. Imbos et al. 227 The reaction of 511 in the presence of catalytic amounts of Pd(OAc)2 and the chiral phosphoramidite 513 gave the 4a-methoxy-4aH-benzo[c]chromen-2(6H)-one 512 in 71% yield with 96% ee. By contrast, the reaction of 511 using BINAP, instead of 513, gave the product 512 in a poor yield with no enantioselectivity.

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