Base Induced l,2-Hydride Shifts from Silicon to Carbon: "Anomalous" Substitution Reactionswith (Halomethyl)diorganosilanes

(C$_6$H$_5$)$_2$Si(H)CH$_2$X (1 a: X = Cl; 1 b: X = I) und C$_6$H$_5$(CH$_3$)Si(H)CH$_2$CI (10) reagieren mit LiOCH$_2$CH$_2$N(CH$_3$)$_2$ (2b) zu den Alkoxysilanen (C$_6$H$_5$)$_2$Si(CH$_3$)OCH$_2$CH$_2$N(CH$_3$)$_2$ (5) bzw. C$_6$H$_5$(CH$_3$)$_2$SiOCH$_2$CH$_2$N(CH$_3$)$_2$ (12). Die Bildung dieser unerwarteten Reaktionsprodukte wird durch einen nucleophilen Angriff des Alkoxids am Si-Atom gedeutet. dem sich eine intramolekulare 1 ,2-Hydridverschiebung vom Si zum C und Eliminierung von Cl e anschließt. Mit weichen Basen, wie z. B. I (-) und (-)SCH$_2$CH$_2$N(CH$_3$)$_2$, wurden dagegen "normale" Substitutionsreaktionen am C-Atom der SiCH$_2$Cl-Gruppe beobachtet(C$_6$H$_5$)$_2$Si(H)CH$_2$X (Ia: X = Cl; 1 b: X = I) and C$_6$H$_5$(CH$_3$)Si(H)CH$_2$CI (10) react with LiOCH$_2$CH$_2$N(CH$_3$)$_2$ (2b) to give the alkoxysilanes (C$_6$H$_5$)$_2$Si(CH$_3$)OCH$_2$CH$_2$N(CH$_3$)$_2$ (5) and C$_6$H$_5$(CH$_3$)$_2$SiOCH$_2$CH$_2$N(CH$_3$)$_2$ (12), respectively. The formation of these unexpected reaction products is interpreted by a nucleophilic attack of the alkoxide at the Si atom, followed by an intramolecular 1 ,2-hydride shift from Si to C and elimination of Cl 8. However, with soft bases [for example l e and (-)SCH$_2$CH$_2$N(CH$_3$)$_2$ "normal" substitution reactions at the C atom of the SiCH$_2$Cl group were observed

What is the role of a-linolenic acid for mammals?

This review examines the data pertaining to an important and often underrated EFA, &alpha;-linolenic acid (ALA). It examines its sources, metabolism, and biological effects in various population studies, in vitro, animal, and human intervention studies. The main role of ALA was assumed to be as a precursor to the longer-chain n-3 PUFA, EPA and DHA, and particularly for supplying DHA for neural tissue. This paper reveals that the major metabolic route of ALA metabolism is &beta;-oxidation. Furthermore, ALA accumulates in specific sites in the body of mammals (carcass, adipose, and skin), and only a small proportion of the fed ALA is converted to DHA. There is some evidence that ALA may be involved with skin and fur function. There is continuing debate regarding whether ALA has actions of its own in relation to the cardiovascular system and neural function. Cardiovascular disease and cancer are two of the major burdens of disease in the 21st century, and emerging evidence suggests that diets containing ALA are associated with reductions in total deaths and sudden cardiac death. There may be aspects of the action and, more importantly, the metabolism of ALA that need to be elucidated, and these will help us understand the biological effects of this compound better. Additionally, we must not forget that ALA is part of the whole diet and should be seen in this context, not in isolation.<br /