Neodymium-catalyzed diene

Dienes are less reactive toward transition metals than enynes and diynes, and perhaps for this reason, the development of effective catalyst systems for the cyclization/hydrosilylation of dienes lagged behind development of the corresponding procedures for enynes and diynes. The transition metal-catalyzed cyclization/hydrosilylation of dienes was first demonstrated by Tanaka and co-workers in 1994. Reaction of 1,5-hexadiene with phenyl-silane catalyzed by the highly electrophilic neodymium metallocene complex Cp 2NdCH(SiMe2)3 (1 mol%) in benzene at room temperature for 3 h led to 5- ///76 -cyclization and isolation of (cyclopentylmethyl)phenylsilane in 84% yield (Equation (15)). In comparison, neodymium-catalyzed reaction of 1,6-heptadiene with phenylsilane led to 5- X(9-cyclization to form (2-methylcyclopentylmethyl)phenylsilane in 54% yield as an 85 15 mixture of trans. cis isomers (Equation (16)). 

Hydrosilation of 1,5- and 1,6-dienes, catalyzed by a chiral neodymium complex, leads to intramolecular bond formation and results in the formation of silylated methylcy-clopentanes (equation 147)538. This reaction is in stark contrast to the reaction catalyzed by group VHI complexes, which gives a range of silanes but no carbocyclic compounds539,540. 

The sequential cyclization/silylation reactions of 1,5-dienes and 1,6-dienes are catalyzed by Cp 2YMe(THF). The reaction tolerates a number of functional groups and proceeds with good yields and diastereoselectivities to give phenylsilane products which can be converted easily to synthetically more versatile alcohols (Scheme 276). The hydrosilylation of dienes is also effectively catalyzed by the neodymium alkyl complex Cp 2NdCH(SiMe3)2. 

Wang reported three-component coupling reaction of aldehydes, amines, and dienes by lanthanide triflate catalyzed aza-Diels-Alder reaction in water [35, 36]. Among lanthanide triflates screened, lanthanum, praseodymium, neodymium, and ytterbium triflate were found to be effective (Table 13.16). It is worth noting that aqueous formaldehyde could be employed as substrate. These reaction conditions were applied in the synthesis of aza-sugars. 

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