Enantioselective total synthesis of valeriananoids A-C

[reaction: see text] The first enantioselective total synthesis of valeriananoids A-C (-)-1-3 is reported starting from the readily available monoterpene (R)-carvone, employing a tandem intermolecular Michael addition-intramolecular Michael addition-alkylation sequence and an electron-transfer-mediated 6-endo-trig cyclization as key steps.     

Models and solution techniques for production planning problems with increasing byproducts

We consider a production planning problem where the production process creates a mixture of desirable products and undesirable byproducts. In this production process, at any point in time the fraction of the mixture that is an undesirable byproduct increases monotonically as a function of the cumulative mixture production up to that time. The mathematical formulation of this continuous-time problem is nonconvex. We present a discrete-time mixed-integer nonlinear programming (MINLP) formulation that exploits the increasing nature of the byproduct ratio function. We demonstrate that this new formulation is more accurate than a previously proposed MINLP formulation. We describe three different mixed-integer linear programming (MILP) approximation and relaxation models of this nonconvex MINLP, and we derive modifications that strengthen the linear programming relaxations of these models. We also introduce nonlinear programming formulations to choose piecewise-linear approximations and relaxations of multiple functions that share the same domain and use the same set of break points in the domain. We conclude with computational experiments that demonstrate that the proposed formulation is more accurate than the previous formulation, and that the strengthened MILP approximation and relaxation models can be used to obtain provably near-optimal solutions for large instances of this nonconvex MINLP. Experiments also illustrate the quality of the piecewise-linear approximations produced by our nonlinear programming formulations.     

Synthesis of (±)‐ar‐Macrocarpene

An efficient first synthesis of the sesquiterpene ar‐macrocarpene, an irregular sesquiterpene isolated from Cupressus macrocarpa foliage, starting from 3‐methylcyclohexenone has been described, which confirmed the structures of macrocarpenes.     

Efficient stepwise and one pot three-component synthesis of 2-amino-4-(2-oxo-2H-chromen-3-yl)thiophene-3-carbonitriles

Environmentally benign conditions have been developed for the synthesis of 2-amino-4-(2-oxo-2H-chromen-3-yl)thiophene-3-carbonitriles (3) starting from 3-acetyl-2H-chromen-2-one (1) through the intermediacy of 2-(1-(2-oxo-2H-chromen-3-yl)ethylidene)malononitrile (2) using the Knoevenagel condensation followed by the Gewald reaction. Alternatively, 3 could also be prepared in a one pot method by treating equimolar amounts of 1, malononitrile, and elemental sulfur. The merits of this preparation are mild reaction conditions, easy work-up procedure, and good yields.     

Asymmetric Synthesis of Highly Substituted β‐Lactones through Oxidative Carbene Catalysis with LiCl as Cooperative Lewis Acid

The reaction of enals with β‐diketones, β‐ketoesters, and malonates bearing a β‐oxyalkyl substituent at the α‐position by oxidative NHC catalysis to provide highly substituted β‐lactones is described. Reactions occur with excellent diastereo‐ and enantioselectivity. The organo cascade comprises two C? C bond formations and one C? O bond formation. Up to four contiguous stereogenic centers including two fully substituted stereocenters are formed in the cascade.     

Locally ideal formulations for piecewise linear functions with indicator variables

In this paper, we consider mixed integer linear programming (MIP) formulations for piecewise linear functions (PLFs) that are evaluated when an indicator variable is turned on. We describe modifications to standard MIP formulations for PLFs with desirable theoretical properties and superior computational performance in this context.     

Synthetic approaches to guanacastepenes. Enantiospecific syntheses of BC and AB ring systems of guanacastepenes and rameswaralide

[reaction: see text] A simple and efficient approach for the BC and AB ring systems of the novel diterpenes guanacastepenes and rameswaralide starting from the readily and abundantly available monoterpene (R)-carvone employing RCM reaction as the key step is described.     

Enantiospecific total synthesis of 15-hydroxy-5-(methoxymethoxy)crinipellin-9-one

Enantiospecific total synthesis of the crinipellin mentioned in the title was accomplished. In the present synthesis cyclopentane ring in campholenaldehyde was identified as the B-ring, two intramolecular rhodium carbenoid CH insertion reactions were employed for the construction of the A and C rings, and an intramolecular Michael addition reaction was utilized for the construction of the D-ring of crinipellin.     

RCM‐Based Approach to (±)‐Cuparene

An efficient approach to the aromatic sesquiterpene cuparene has been described starting from the readily available β‐ionone and employing a combination of epoxide rearrangement‐based ring‐contraction and ring‐closing metathesis reactions as key steps.     

Simultaneous planar measurement of droplet velocity and size with gas phase velocities in a spray by combined ILIDS and PIV techniques

A new approach for simultaneous planar measurement of droplet velocity and size with gas phase velocities is reported, which combines the out-of-focus imaging technique ‘Interferometric Laser Imaging Droplet Sizing’ (ILIDS) for planar simultaneous droplet size and velocity measurements with the in-focus technique ‘Particle Image Velocimetry’ (PIV) for gas velocity measurements in the vicinity of individual droplets. Discrimination between the gas phase seeding and the droplets is achieved in the PIV images by removing the glare points of focused droplet images, using the droplet position obtained through ILIDS processing. Combination of the two optical arrangements can result in a discrepancy in the location of the centre of a droplet, when imaging through ILIDS and PIV techniques, of up to about 1 mm, which may lead to erroneous identification of the glare points from droplets on the PIV images. The magnitude of the discrepancy is a function of position of the droplet’s image on the CCD array and the degree of defocus, but almost independent of droplet size. Specifically, it varies approximately linearly across the image along the direction corresponding to the direction of propagation of the laser sheet for a given defocus setting in ILIDS. The experimental finding is supported by a theoretical analysis, which was based on geometrical optics for a simple optical configuration that replicates the essential features of the optical system. The discrepancy in the location was measured using a monodisperse droplet generator, and this was subtracted from the droplet centres identified in the ILIDS images of a polydisperse spray without ‘seeding’ particles. This reduced the discrepancy between PIV and ILIDS droplet centres from about 1 mm to about 0.1 mm and hence increased the probability of finding the corresponding fringe patterns on the ILIDS image and glare points on the PIV image. In conclusion, it is shown that the proposed combined method can discriminate between droplets and ‘seeding’ particles and is capable of two-phase measurements in polydisperse sprays.