Pyridine 2,6-dimethyl-: bulky base

The incorporation into anti-parallel DNA of a cross-linked Watson-Crick base pair (120) has been described, " though no data for the duplexes formed are provided. A dissociable covalently bonded base pair (121), modelled to impose minimal distortion of the duplex, was used to replace a Watson-Crick base pair in ODNs. The second (complementary) strand was introduced by ligation of appropriate ODNs. The un-natural base pair between 2-amino-AT -dimethyl-purine and pyridin-2-one has been developed for specific transcription. " The ribo-triphosphate of pyridin-2-one and the 5-methyl derivative are selectively incorporated opposite 2-amino-Ar -dimethyl-purine by T7 RNA polymerase. The bulky dimethyl group prevents recognition and pairing by the natural bases. 

A widely used class of compounds are pyridine and alkylpyridines, including 2,6-lutidine, 2,4,6-coUidine, DTBP, quinoline, 4-methylquinohne, and 2,4-dimethyl-quinoline (565,582). These molecules interact with acidic hydroxyls through their N-atoms with formation of protonated species. Because they are strong bases, the possibility to extract protons from their original positions cannot be ruled out. An advantage (but in some cases disadvantage) of many pyri dines with bulky substituents is that, for steric reasons, they do not interact with Lewis acid sites through the N-atoms, or this interaction at least is hindered. 

Inspired by the well-established principles in oxidation catalysis with heme complexes, Gomez et al. designed a new catalyst platform based on modifications at the well-known mep and mcp ligands (mcp = iVA -dimethyl-A[,A[ -bis (2-pyridylmethyl)-cyclohexane-1,2-diamine) by introducing bulky pinene groups at positions 4 and 5 of the pyridine rings [64]. By doing so, [Fe(OTf)2((5,5,R)-mcpp)], [Fe(OTf)2((/ ,/ ,/ )-mcpp)], and [Fe(OTf)2((/ )-mepp)] complexes were synthesized (Scheme 17). 

In 2012, Maes and co-workers reported a new transition-metal-catalyzed methodology for the direct C2-H functionalization of piperidines [67], via pyridine-directed Ru-catalyzed C(sp )-H alkylation with alkenes [68]. Based on previous work [69-73], they discovered that a combination of a bulky alcohol (2,4-dimethyl-3-pentanol) and a catalytic amount of a carboxylic acid [74] is necessary to avoid side reactions such as isomerization and/or reduction of the alkene reactant (Scheme 11). They successfully applied this method to the total synthesis of ( )-... 

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