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Second‐Generation Trifluoromethyl‐Substituted Chiral Dendrimers Containing Triply Branched Building Blocks: CF 3 as sensitive NMR probe for ‘remote’ diastereotopicity
Author(s) -
Greiveldinger Guy,
Seebach Dieter
Publication year - 1998
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19980810515
Subject(s) - dendrimer , chemistry , trifluoromethyl , stereochemistry , nuclear magnetic resonance spectroscopy , aldol reaction , triol , biphenyl , diastereomer , proton nmr , polymer chemistry , organic chemistry , catalysis , diol , alkyl
( S )‐4,4,4‐Trifluoro‐3‐hydroxybutanoic acid was used as a starting material for the synthesis of dendritic branches ( 16 – 21 , 30 – 32 ) which were attached to a chiral triol ( 6 or ent ‐ 6 ), derived from ( R )‐3‐hydroxybutanoic acid, to give CF 3 ‐substituted dendrimers ( 33 – 36 , 38 – 40 ) and dendritic compounds ( 37 ) of 1st and 2nd generation. The key steps in these syntheses are diastereoselective aldol additions of dioxanone enolates (building blocks and intermediates 6 – 15 , 22 , 23 , and 25 – 28 ) and Williamson etherifications of benzylic‐branch bromides with triols (intermediates and products 16 – 21 , 28 , and 30 – 40 ). The surfaces of the dendrimers are covered with MeO ( 33 – 35 , 38 – 40 ) or allyloxy groups ( 36 and 37 ). The new dendrimers are characterized by NMR and mass spectroscopy. 19 F‐NMR Signals of the CF 3 groups reveal constitutional heterotopicities caused by substituents which are separated from the F‐nuclei by up to 15 bonds (through a 1,1′‐biphenyl‐4,4′‐diyl spacer!) ( Fig. 6 ).