Ruthenium-Catalyzed MCRs

1 Intermolecular Alkyne Cyclotrimerization The cyclotrimerization of three different alkynes to give Unear products have been described mainly using Ni-based catalysts (see Section 3.3.1) [51, 52]. Nevertheless, Yamamoto 

SCHEME 3.73 Four-component Fe(II)-catalyzed synthesis of branched amines. 

SCHEME 3.74 Iron-catalyzed 1,2-addition of ammonium ylides to P,y-unsaturated a-ketoesters. 

SCHEME 3.76 Proposed mechanism for the Ru(ll)-catalyzed intermolecular cyclotrimerization of alkynes. 

SCHEME 3.77 Ru-catalyzed three-component synthesis of pyrroles. 

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Cross-Enyne Metathesis/Diels-Alder MCRs Ruthenium-based complexes are known to catalyze the metathesis between alkynes and alkenes to afford 1,3-dienes. Fnstero, del Pozo et al. further exploited this cross-enyne metathesis (CEYM) by trapping the 1,3-diene with a dieno-phile via an intermolecnlar Diels-Alder reaction [198]. Thns, the Ru-catalyzed MCR between alkynes 220-221 and 1,7-octadiene as an in situ sonrce of ethylene by RCM generates a 1,3-diene that can snbseqnently nndergo a Diels-Alder reaction with a wide variety of dienophiles 222... 

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