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Enyne, yttrium-catalyzed

Molander has developed effective protocols for the cyclization/hydrosilylation of 1,6-enynes catalyzed by lanthanide metallocene complexes/ For example, reaction of cyclohexyl-substituted 1,6-enyne 15a with phenylsilane catalyzed by Cp 2YMe(THF) in cyclohexane at room temperature for 2h gave silylated alkylidene cyclopentane 16a as a 6.5 1 mixture of trans. cis isomers (Table 5, entry 1). The diastereoselectivity of the reaction depended strongly on the nature of the allylic substituent. For example, yttrium-catalyzed cyclization/ hydrosilylation of the ethyl-substituted enyne 15b gave silylated cyclopentane 16b in 88% yield as a single diastereomer (Table 5, entry 2). [Pg.377]

Yttrium-catalyzed enyne cyclization/hydrosilylation was proposed to occur via cr-bond metathesis of the Y-G bond of pre-catalyst Cp 2YMe(THF) with the Si-H bond of the silane to form the yttrium hydride complex Ig (Scheme 8). Hydrometallation of the C=G bond of the enyne coupled with complexation of the pendant G=G bond could form the alkenylyttrium alkyl complex Ilg. Subsequent / -migratory insertion of the alkene moiety into the Y-C bond of Ilg could form cyclopentylmethyl complex Illg. Silylation of the resulting Y-C bond via cr-bond metathesis could release the silylated cycloalkane and regenerate the active yttrium hydride catalyst. Predominant formation of the /ra //j--cyclopentane presumably results from preferential orientation of the allylic substituent in a pseudo-equatorial position in a chairlike transition state for intramolecular carbometallation (Ilg —IHg). [Pg.377]

Table 5 Yttrium-catalyzed enyne cyclization/hydrosilylation... Table 5 Yttrium-catalyzed enyne cyclization/hydrosilylation...
Lanthanide-catalyzed enyne cyclization/hydrosilylation was also applied to the synthesis of silylated alkylidene cyclohexane derivatives. For example, reaction of the 3-silyloxy-l,7-enyne 17 with methylphenylsilane catalyzed by Gp 2YMe(THF) at 50°G for 8h gave 18 in quantitative yield as a 4 1 mixture of trans cis isomers (Equation (11)). Employment of methylphenylsilane in place of phenylsilane was required to inhibit silylation of the initially formed yttrium alkenyl complex, prior to intramolecular carbometallation (see Scheme 8). [Pg.378]


See other pages where Enyne, yttrium-catalyzed is mentioned: [Pg.379]    [Pg.120]    [Pg.465]   


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