Preparation of Substrates Epoxidation of a,b-unsaturated esters

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Presentation transcript:

Preparation of Substrates Epoxidation of a,b-unsaturated esters EPOXIDATION OF UNSATURATED ESTERS. SYNTHESIS OF TRISUBSTITUTED GAMMA-BUTYROLACTONES Santiago Rodríguez*, Florenci V. González, Javier Izquierdo, Irakusne López, Raül Portolés Departament de Química Inorgànica i Orgànica, Universitat Jaume I, Castelló, Spain email: rodrigue@qio.uji.es a,b-Epoxyesters are versatile functionalities in organic synthesis since they can be converted into interesting synthetic compounds through the opening of the oxirane ring1,2. The most convenient method for their preparation is through epoxidation of unsaturated esters using a hydroperoxide in the presence of a base. A deeper understanding of the stereoselectivity of the epoxidation of unsaturated esters would increase the synthetic applications of these intermediates. Introduction Preparation of Substrates The g-hydroxy-a,b-unsaturated esters 1 were obtained by treatment of ethyl (E)-4-oxo-2-butenoate with the corresponding Grignard reagent2. Ethyl (E)-4-oxo-2-butenoate was prepared from furoic acid through a three steps sequence. Butyrolactone synthesis Epoxide stereochemistry Epoxidation of a,b-unsaturated esters Reagent Solvent T(ºC)/t 2:3 Yield(%) TBHP, EtLi THF -20/20h 70:30 60 TBHP, EtLi, TMEDA 88:12 50 THF/HMPA 42 TBHP, Et2Zn CH2Cl2 0/120h 20:80 15 CMHP, EtLi 77:23 65 4 R= Ph Results •The stereoselectivity does not depend on the nature of R group furnishing mainly syn isomer 2 (using TBPLi) •A cation scavenger or a more polar solvent increase the selectivity •Zn peroxide reverses the selectivity •Lactones are obtained under Sharpless’ conditions3 using buffered sodium thiophenolate •Stereochemical assignment of the lactones was performed by NOE experiments and x-ray References Acknowledgments 1. Chong, J.M.; Sharpless, K.B. Tetrahedron Lett. 1985, 26, 4683-4686 2. Rodríguez, S.; Vidal, A.; Monroig, J.J.; González, F.V. Tetrahedron Lett. 2004, 45, 5359-5361. 3. Behrens, C.H.; Sharpless, K.B. J.Org.Chem. 1985, 50, 5696-5704 This work was financed by Conselleria d’Educació, Cultura i Ciència de la Generalitat Valenciana (GV05/071) and Bancaixa-UJI foundation (P1 1A2005-14).