Enantioselective synthesis of proline derivatives by 1,3-dipolar cycloadditions

Research devoted to the synthesis of highly substituted prolines, which are hepatitis C virus inhibitors, using 1,3-dipolar cycloadditions (1,3-DC) of azomethine ylides is described. In the first part, a diastereoselective approach using an inexpensive lactate-derived acrylate as dipolarophile is described. In the second part, our efforts using simple and easily accessible chiral silver(I) and gold(I) complexes as catalysts for enantioselective synthesis of proline derivatives are reviewed. In this case, chiral phosphoramidites and binap have been used as privileged ligands. Parallel to these experimental results, considerable effort was dedicated to run semiempirical density functional theory (DFT) calculations to explain and justify the stereoselectivity of each process.This work has been supported by the DGES of the Spanish Ministerio de Ciencia e Innovación (MICINN) (Consolider INGENIO 2010 CSD2007-00006, FEDER-CTQ2007-62771/BQU, and by the Hispano-Brazilian project PHB2008-0037-PC), Generalitat Valenciana (PROMETEO/2009/039), and by the University of Alicante (GITE-09020-UA)

The fracture toughness of a ultrahigh carbon steel containing 1.5 wt% C

Thermomechanical processing of ultrahigh-carbon steels allows the attainment of spheroidized and pearlitic microstructures that show very different mechanical properties. Spheroidized microstructures are formed by proeutectoid and eutectoid carbide particles embedded in a ferrite matrix. The mean proeutectoid carbide particle size is larger than the mean eutectoid carbide particle size and is practically invariable with austenitizing temperature below 850 °C. Pearlitic microstructures exhibit prior austenite grain sizes and pearlite colony sizes which increase and interlamellar spacings which decrease as the austenitizing temperature increases above 850 °C. A proeutectoid carbide size distribution that remains basically constant with austenitizing temperature is also observed in these microstructures. Plane-strain fracture toughness of spheroidized and pearlitic UHCS-1.5C materials do not vary significantly with austenitizing temperature, being the average fracture toughness of about 40 MPa m1/2 and 30 MPa m1/2, respectively. The constancy of fracture toughness with austenitizing temperature of the spheroidized microstructures is attributed to the constancy of the mean proeutectoid and eutectoid carbide size. Austenite grain size, pearlite colony size, interlamellar spacing and undissolved proeutectoid carbide size are evaluated for the influence of fracture toughness associated with pearlitic microstructures. It is found that proeutectoid carbide is the microstructural parameter that controls fracture toughness of pearlitic microstructures. Austenite grain size, pearlite colony size and interlamellar spacing are considered to have a minor influence.Peer reviewe