Aryl branch

More recently, Mullen et al. have worked out very efficient procedures to generate highly arylaled, branched oligo(phcnylcne) and related oligo(arylcne) derivatives following different synthetic approaches. 

Mukaiyama Michael reactions of alkylidene malonates and enolsilanes have also been examined (244). The stoichiometric reaction between enolsilane (342a) and alkylidene malonate (383) proceeds in high selectivity however, catalyst turnover is not observed under these conditions. The addition of HFIP effectively promotes catalyst turnover, presumably by protonation and silyl transfer from the putative copper malonyl enolate generated in this reaction. The reaction proved general for bulky P-substituents (aryl, branched alkyl), Eq. 209. 

Scheme 4.11. Construction of 1 — 2 aryl-branched poly esters via phenol acylation.

After debenzylation (Pd-C, cyclohexene) of the hypercores (e.g., 25) by transfer hydrogenation, they were treated with aryl branched, benzyl ether dendrons (Scheme 5.6) that were prepared by similar iterative transformations,1271 i.e., benzylic bromination and phenolic O-alkylation (See Section 5.4.2). Thus, hexaphenol core 27 was reacted with six equivalents of the benzylic bromide building block 28 to give the benzyloxy terminated dendrimer 29. Key features of these dendrimers include cores with flexible alkyl spacers and a three-directional, quaternary carbon branching center. 

Brunner and Fiirst[431 reported the synthesis of a series of optically active, extended chelate phosphines, one of which was derived from the reaction of 5-bromo-l,3-di(bor-neoxymethyl)benzene (69) and bis(dichlorophosphino)methane (70). Technically, the product (-)-l,l-bis 3, 5 -di(borneoxymethyl)phenyl]phosphino methane (71) is both a first tier P- and 1,3-aryl-branched dendrimer. Excluding distortions, the maximum distance between the P atom and the most distant H atom(s) is 11.9 A for the two-layer ligand 71. The Rh-catalyzed [Rh(cod)Cl]2) hydrogenation of (a)-/V-acetamidocinnamic acid in the presence of 71 afforded a disappointingly low [5.2 % ee (/ )] optical induction. 

Pseudoephedrine amides with a wide variety of a-substituents, including aryl, branched alkyl,i" chloro, fluoro (described in... 

Aromatic Claisen rearrangements in 2,3-unsaturated sugar systems are useful for the stereo-controlled synthesis of aryl-branched sugars [87] (O Scheme 20). The a-anomer 97 is much less reactive in comparison to the /3-anomer 99. This thermal rearrangement is carried out by refluxing in iV,iV-diethylaniline. The efficiency of the reaction is almost independent of the nature of the p-substituent in the phenyl group. 

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