Catalysis, continued derivatives

A set of core-functionalized dendrimers was synthesized by Van Leeuwen et al. and one compound was applied in continuous catalysis. [45] The dendritic dppf, Xantphos and triphenylphosphine derivatives (Figures 4.22, 4.30 and 4.31) were active in rhodium-catalyzed hydroformylation and hydrogenation reactions (performed batch-wise). Dendritic effects were observed which are discussed in paragraph 4.5. The dendritic rhodium-dppf complex was applied in a continuous hydrogenation reaction of dimethyl itaconate. 

Disubstituted dihydropyrans are produced with high u/iri-selectivity when 2-phenyl-4-(4-tolylsulfonyl)-3,4-dihydro-2H -pyrans ate treated with Al-based Lewis acids <99SL132>. Tetraenes 10, derived from dienes via their epoxides, undergo a double RCM reaction under Ru-catalysis to yield polycyclic ethers 11 in which the dihydropyran units can be joined by a variable number of carbon atoms <99JOC3354>. Continued work on the use of dispiroketals in synthesis has led to an improved route to the enantiomers of bi(dihydropyrans) 12 <99JCS(P1)1639>. 

Typical phase transfer catalysis in liquid-liquid systems combines processes in which Na+ or K+ salts of inorganic and organic anions derived from strong adds (phenolates, thiolates, carboxylates, etc.) are continuously transferred from aqueous (often alkaline) solutions to the organic phase by the phase transfer catalysts. Applications include nucleophilic substitution, addition, elimination, oxidation, and reduction reactions. 

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