Asymmetric synthesis, conformational analysis, chiroptical properties and absolute configuration of some 3-phenylcycloalkanones

ASYMMETRIC SYNTHESIS , CONFORMATIONAL ANALYSIS, CHIROPTICAL PROPERTIES AND ABSOLUTE CONFIGURATION OF SOME 3-PHENYLCYCLOALKANONES Patrizia Scafatoa), Francesca Capriolia), Giovanna Longhib), Sergio Abbateb), .., Giuseppe Mazzeoa), Carlo Rosinia) aDipartimento di Chimica, Università della Basilicata, via N. Sauro 85, Potenza, ITALY, (gi.mazzeo@tiscali.it); b indirizzo di Brescia In the last 10-15 years the development of computational chemistry guaranteed the reliable calculation of electronic and vibrational chiroptical properties and then a (generally) safe assignment of the molecular absolute configuration [1]. A main difficulty is represented by the flexible molecules: the rotation around a single bond connecting a stereogenic center and a Phenyl group constitutes a significant example, as pointed out by Stephens [2] and others [3], even if (quite an interesting effect) this feature could be responsible [3b] of characteristic VCD signals which can constitute a direct probe of the AC. In order to explore in deep this interesting point the three 3-phenylcycloalkanones below have been prepared, their chiroptical properties (ORD, ECD, VCD) measured and studied by means of DFT methods. Compounds 1-3 have been prepared in high yield and enantiomeric excess, by the asymmetric addition of 3-phenylboronic acid to the corresponding cycloalkenone in the presence of our phosphoroamidite tropos ligand [4] or the well-known binaphtylphosphine BINAP. ORD (hexane) values range from –48 to –202 going from 589 to 405 nm for 1 and from –20 to –158 for 2. (Mancano dati sperimentali per 3, 3-fenilcicloeptanone). TDDFT/B3LYP/6-31G* calculations on DFT/B3LYP/6-31G* geometries provide ORD curves between –155 and –724 for 1 and –102 and –494 for 2, i.e. the theoretical values are correct in sign and order of magnitude even if five times larger than the experimental ones. Use of the more extended aug-cc-pVDZ basis set does no improve so much the agreement between theoretical/experimental figures. [1] Crawford, T.D., Theor. Chem. Acc. 2006, 115, 227-245. [2] Stephens, P. J.; Devlin, F. J.; Cheeseman, J. R.; Frisch, M. J. Chirality 2002, 14, 288-296. [3] a) Giorgio, E.; Parrinello, N.; Caccamese, S.; Rosini, C. Org. Biomol. Chem., 2004, 2, 3602-3607; b) vostro lavoro naringenina. [4] Scafato, P.; Cunsolo, G.; Labano, S.; Rosini, C. Tetrahedron 2004, 60, 8801-8806.