Advances in the stereoselective synthesis of antifungal agents and ...

Chapter 4 99NNH37CO2EtOH(±)-27a(+)-27aDEAD/ PPh 3NNCO 2 Et(±)-41a = 5 Substituted(±)-41b = 4 Substitutedrelative ratio (±)-41a /(±)-41b 3:1Scheme 4.5: Mitsunobu reaction with 4(5) ethyl imidazole carboxylate 37.The structural assignment of the two regioisomers (±)-41a,b wasachieved by monodimensional 1 H and 13 C-NMR and two dimensional onebond 1 H- 13 C correlation spectra. From these experiments it was possibleto assign the benzhydryl and the imidazole methynes, while long range 1 H-13C-correlation spectra were used to assign the position of the carboethoxygroup on the imidazole ring (Fig. 4.2).Benzhydrylic proton AImidazole methyne proton BNImidazole proton and carbon CNCO 2 EtCarbethoxy groupImidazole proton and carbon DFigure 4.2: representative protons and carbons of 41a,b for the assignment of regiochemistry.In the case of (±)-41a the benzhydrylic proton (proton A fig.4.2)showed a long range correlation only with one of the imidazole methynes (position B and C fig.4.2). For (±)-41b the correlation was found with boththe methynes of the imidazole ring ( position B or C fig.4.2). These results