Thiopyran route to polypropionates : increasing stereochemical diversity of aldol adducts

Linear carbon-carbon chains with alternating hydroxyl and methyl substituents are a common motif in various natural products. Many of these so-called polypropionates show biological activity and are useful in the fields of medicine and agriculture. The stereoselective synthesis of polypropionates has been extensively investigated and numerous strategies and tactics have been developed. The sequential aldol reactions of thiopyran derivatives 122 and 125 followed by desulfurization of aldol adducts is a strategy to rapidly construct hexapropionate synthons (e.g. 165). The present work concerns the control of the stereoselectivity in the two key aldol coupling steps inherent in this strategy. In Section 2.2, the influence of reaction conditions and the relative configuration of the â-alkoxy group of aldehydes cis-125b and trans-125c on the diastereoselectivity of the 1st aldol coupling are discussed. The results were rationalized according to Evan's merged 1,2- and 1,3-stereoinduction model (nonchelation), with the exception of the MgBr2•OEt2 promoted reactions of 137b (M = TMS) with 125a, 125b and 125c, which were accommodated by assuming chelation control. Under appropriate conditions, three (126a-128a) of the four possible diastereomers could be obtained stereoselectively. The fourth diastereomer (129a) was readily available by isomerization (vide infra). In Section 2.3, the diastereoselectivities of the aldol reactions of (±)-125a with (±)-126a and (±)-127a (previous work) and reactions of (±)-125a with (±)-128a and (±)-129a (this work) are presented. These reactions occurred with high mutual kinetic enantioselection (MKE) and were highly diastereoselective for the formation of one out of eight possible diastereomers. The diastereoselectivity of aldol reactions of (±)-125a with related â-alkoxy ketones (±)-166 and (±)-168 (previous work) and reactions with enantioselection (MKE) and were highly diastereoselective for the formation of one out of eight possible diastereomers. The diastereoselectivity of aldol reactions of (±)-125a with related â-alkoxy ketones (±)-166 and (±)-168 (previous work) and reactions with (±)-172 and (±)-174 (this work) were also investigated. Contrary to the aldol reactions of â-hydroxy ketones (126a-129a), reactions of â-alkoxy ketones (166, 168, 172, 174) proceeded without significant MKE. These reactions were also highly diastereoselective giving two products, one each from the like and unlike reactions. In Section 2.4, the use of imidazole as an effective catalyst for syn/anti isomerization of aldols via keto-enol tautomerism is described. A large variety of aldol (e.g. 126) and bisaldol (e.g. 165) adducts were shown to undergo efficient isomerization with minimal retroaldol and elimination reactions. The rate constants for this process were determined for several substrates. It was found that thiopyranone derived aldols isomerize much faster than related cyclohexanone aldols and the â-hydroxy ketones (e.g. 128a) isomerize faster than â-alkoxy derivatives (e.g. 172). In section 2.5, the relative configuration of aldol adducts was rigorously determined using chemical correlations and NMR methods

Some results and problems on clique coverings of hypergraphs

For a $k$-uniform hypergraph $F$ we consider the parameter $\Theta(F)$, the minimum size of a clique cover of the of $F$. We derive bounds on $\Theta(F)$ for $F$ belonging to various classes of hypergraphs.Comment: 14 page

Colouring versus density in integers and Hales-Jewett cubes

We construct for every integer $k\geq 3$ and every real $\mu\in(0, \frac{k-1}{k})$ a set of integers $X=X(k, \mu)$ which, when coloured with finitely many colours, contains a monochromatic $k$-term arithmetic progression, whilst every finite $Y\subseteq X$ has a subset $Z\subseteq Y$ of size $|Z|\geq \mu |Y|$ that is free of arithmetic progressions of length $k$. This answers a question of Erd\H{o}s, Ne\v{s}et\v{r}il, and the second author. Moreover, we obtain an analogous multidimensional statement and a Hales-Jewett version of this result.Comment: 5 figure

Quality of child health care in the family health strategy

OBJECTIVE: to verify the quality of child health care in the Family Health Strategy (FHS) in a state capital of Northeastern Brazil. METHODS: a descriptive study using a quantitative approach was carried out in 2010 with 66 primary care (PC) teams represented by their doctors and nurses. The survey used part of the Evaluation for Quality Improvement of the Family Health Strategy² (AMQ), a self-rating instrument of the Brazilian Ministry of Health which evaluates the FHS actions and services and classifies them by the following quality-based standards of care: Elementary, undergoing development, Consolidated, Good or Advanced. RESULTS: 84.1% of the FHS-teams rated themselves as providing "Elementary" actions and services, and 47.7% of them considered that they provided "Advanced" ones. The health teams with less than four years of implementation rated themselves better. CONCLUSION: these findings suggest that most of the FHC-teams are providing care with an elementary standard of quality, and indicate that better quality child care is apparently delivered with by teams with less time of implementation

The wage penalty of smoking in Brazil: evidence from the Special Survey on Tobacco Addiction

The aim of this study is to investigate the hypothesis that smoking reduces earnings. We use data from the Special Survey on Tobacco Addiction, which was jointly carried out with the 2008 Brazilian National Household Sample Survey. Our results support the hypothesis that smoking reduces wages. Furthermore, we found that about two-thirds of wage differential between male smokers and non-smokers is due to observable characteristics.O principal objetivo deste artigo é analisar a hipótese de que o tabagismo reduz os rendimentos do trabalho. Utilizamos dados da Pesquisa Especial de Tabagismo (PETab) realizada durante a PNAD 2008. Nossos resultados sustentam a hipótese de que fumar cigarro afeta negativamente o salário. Além disso, encontramos que as características observáveis explicam aproximadamente dois terços do diferencial salarial observado entrehomens fumantes e não-fumantes