Highly enantioselective propargylic monofluorination established by carbon-13 and fluorine-19 NMR in chiral liquid crystals

Correlation 2D‐NMR experiments involving both 13C and 2H isotopes in oriented media: methodological developments and analytical applications

“…Alternatively, NMR techniques avoiding any chemical modifications of molecules were explored to overcome this limitation. These methods include proton‐decoupled 19 F ( 19 F–{ 1 H}) NMR for fluorinated compounds or the 13 C–{ 1 H} NMR, which is applicable for all isotopically unmodified organic and organometallic compounds. In this latter approach, the 13 C i sites of enantiomers or the enantiotopic 13 C i sites can be spectrally differentiated on the basis of 13 C CSA's according to Eqn (2) …”

The propargylic route as efficient entry to monofluoro and gem-difluoro compounds: mechanistic considerations

“…The last model, alcohol 13 having an hydrogen on the acetylenic terminal carbon, was prepared in a 90% ee. Here again the reaction with DAST at À50 8C was highly stereoselective affording 14 in 88% ee [11].…”

“…The second model 11 had an alkyl group on the acetylenic carbon and was prepared with a ee higher than 95%. In that case the dehydroxy-fluorination reaction had a lower stereocontrol, which was highly temperature dependent: at À40 8C it gave the fluoride 12 in a low 45% ee and even at very low temperature (T ¼ À95 8C) the reaction was moderately stereoselective affording 12 in a 75% ee only (as established by NMR in chiral liquid crystals) [11]. The last model, alcohol 13 having an hydrogen on the acetylenic terminal carbon, was prepared in a 90% ee.…”

Chemical shift anisotropy edited complete unraveling of overlapped 1H NMR spectra of enantiomers: Application to small chiral molecules

“…The recent study also discusses the use of homo and heteronuclear two-dimensional methods to analyse a mixture of deuterated unlike and like stereo isomers [12]. There are also studies using 13 C [13,14] and 19 F [15,16]. In spite of severe overlap of the transitions, the proton detection is advantageous because of; (a) its high magnetic moment, (b) high natural abundance and (c) abundant presence in all the chiral organic molecules.…”