Thermal electrocyclization reactions II: benzooctatetraenes and benzodecapentaenes

Thermal electrocyclization reactions of benzooctatetraenes and benzodecapentaenes substituted with R=H, Cl, and methyl were studied experimentally and computationally. Methyl and unsubstituted benzooctatetraenes and benzodecapentaenes give the [4.2.0]bicyclooctadiene products by 8π,6π-electrocyclization. Chlorine substitution led to thermal rearrangement of the initially formed 8π,6π-electrocyclization intermediates to give unprecedented products.     

Invertibility of a linear combination of two matrices and partial orderings

In this paper, we present some results relating different matrix partial orderings and the invertibility of a linear combination of EP matrices.     

New results on (b,c)–inverses

In this paper, we present some necessary and sufficient conditions for the existence of the (b, c)-inverse and several representations for the (b, c)-inverse related to the group inverse. Since Mary inverse, core inverse, dual core inverse and Bott–Duffin (e, f)-inverse are all the special cases of the (b, c)-inverse, related results for these inverses are obtained.     

Oxidative 10-membered ring expansion and contraction of stereoisomeric 1(10)-unsaturated and 1,10-epoxy-5-oxo-5,10-secosteroids induced by peracids

The present study is concerned with the oxidative behaviour of unsaturated and epoxy 5-oxo-5,10-secosteroids in the presence of m-CPBA or TFAA-UHP as oxidants in order to investigate potential parameters controlling the chemoselectivity and regioselectivity. In the study we discovered a striking difference in the chemical behaviour of stereoisomeric compounds, (Z)- and (E)-3β-acetoxy-5,10-secocholest-1(10)-en-5-ones, as well as 1S,10R- and 1R,10R-epoxides. The secoketones were oxidized with exclusively C-6 migration and Baeyer–Villiger rearrangement product formation, whereas their stereoisomers provided the ring-contracted products, without lactone formation. The preferred conformation of expanded and contracted rings was established by NOESY correlations. The structures of two obtained lactones were also confirmed by X-ray analysis. The mechanistic and stereochemical aspects of these transformations are discussed.     

Quantification of (−)-Epicatechin and Procyanidin B2 in Chocolates

JPC – Journal of Planar Chromatography – Modern TLC - Validation of a method for the quantification of (−)-epicatechin and procyanidin B2 in chocolates is reported. After a simple...     

Sturm theorems for second order linear nonhomogenous differential equations and localization of zeros of the solution

It is shown that Sturm theorems, formulated in the 1830??s ([1], [2], [3] and [4]) and valid for second order linear homogeneous differential equation L(y)??y??+a(x)y??+b(x)y=0, could as well be formulated for the class of nonhomogeneous linear differential equations L(y)=f(x). Criteria for the existence of oscillatory solutions of nonhomogeneous equations, as well as more exact locations of the zeros are given.