Acyclic -secondary alcohols

In comparison to the N- and S-counterparts, alkoxides possess lower nucleophilicity. Therefore, the reductive elimination process to form the C—O bond is much slower than those to form C— N and C—S bonds [103]. Palucki, Wolfe and Buchwald developed the first intramolecular Pd-catalyzed synthesis of cyclic aryl ethers from o-haloaryl-substituted alcohols [104]. For example, 3-(2-bromophenyl)-2-methyl-2-butanol (91) was converted to 2,2-dimethylchroman (92) under the agency of catalytic Pd(OAc)2 in the presence (S)-(-)-2,2 -bis(di-p-tolylphosphino)-l,r-binaphthyl (Tol-BINAP) as the ligand and K2CO3 as the base. The method worked well for the tertiary alcohols, moderately weE for cychc secondary alcohols, but not for acyclic secondary alcohols. 

Kinetic Resolution by Hydrolysis. Until very recently, kinetic resolution of racemic alcohols as ester derivatives was by far the most common type of asymmetric transformations involving lipases. There are number of examples involving acyclic secondary alcohols, such as the glyceraldehyde derivative in eq 1 and various related alkyl- and aryloxy substituted chloride and tosylate glycerol derivatives. - ... 

Kinetic Resolution of Racemic Secondary Alcohols. Racemic cyclic and acyclic secondary alcohols and p-halohydrins are kinetically resolved in good chemical yields with modest-to-excellent enantioselectivity (eqs 2 and 3). 

Table 11.1-15. Lipase-catalyzed enantiomer-differentiating hydrolysis of esters of racemic acyclic secondary alcohols in aqueous solution (CCL Candida cylindracea lipase, PSL Pseudomonas sp. lipase, PFL Pseudomonas fluorescens lipase, PAL Pseudomonas aeruginosa lipase, ASL Alcaligenes sp. lipase, ANL Aspergillus niger lipase, PCL Pseudomonas cepacia lipase, ROL Rhizopus oryzae lipase,...

Numerous acyclic secondary alcohols have been separated into their enantiomers using lipase-catalyzed acyl-transfer [187]. As long as the substituents are different in size, excellent selectivities were obtained with lipases from Candida antarctica (CAL) and Pseudomonas sp. (PSL) [188]. 

Pyridines and quinolines are prepared via dehydrogenative coupling of y-aminoalcohols and secondary alcohols in the presence of a bipyridyl-based ruthenium pincer complex (Scheme 6) (13CC6632). A number of cyclic and acyclic secondary alcohols were tolerated under these conditions. 

Chiral 2-azadamantane-N-oxyls can also be used for kinetic resolution of secondary alcohols via asymmetric oxidation [131]. S-Factors of up to 82.2 were achieved for a range of cyclic and acyclic secondary alcohols using aza-adamantane catalyst 44 (Scheme 19.22). 

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