Oxido Groups Research Articles

ChemInform Abstract: A HIGHLY STEREOSELECTIVE SYNTHESIS OF TRISUBSTITUTED ETHYLENES FROM α‐(TRIALKYLSILYL) KETONES

AbstractBei der Umsetzung der Trialkylsilylketone (I) mit MeLi/THF bei ‐78°C bilden sich Gemische, die die Isomeren (II) und (III) enthalten; Behandlung der Gemische mit KO‐tBu bzw. mit Säure verläuft stereoselektiv unter syn‐ bzw. anti‐Eliminierung und Bildung des (E)‐Olefins (IV) bzw. des (Z)‐Isomeren (V).

A Highly Stereoselective Synthesis of Trisubstituted Ethylenes from α-Trialkylsilyl Ketones

Abstract A novel procedure for preparing trisubstituted ethylenes stereoselectively is based on the reaction of α-trialkylsilyl-substituted ketones with alkyllithium reagents and on the following highly discriminative elimination of the silyl and oxido (or hydroxyl) groups from the resulting adducts. The syn-elimination of both groups is observed under basic conditions, while the reaction proceeds in anti-fashion on acid treatment. Furthermore α-trimethylsilylated ketones are shown to be readily obtained from 2-trimethylsilyl-2,3-dialkyloxiranes. The reaction sequence is applied to the stereoselective synthesis of tetrahomonerol which has been obtained from the codling moth.

Reactions of N-heteroaromatic bases with nitrous acid. Part 5. Kinetics of the diazotisation of substituted 2-aminopyridine and 2-aminopyridine 1-oxide

In perchloric acid (up to 3.0M) kept at constant ionic strength the diazotisation of 2-amino-5-methylpyridine and 2-amino-5-chloropyridine.1-oxide takes place mainly by the interaction of the nitrous acidium ion with the protonated form of the former and the free form of the latter. However, the diazotisation of 2-amino-5-chloropyridine and 2-amino-5-methylpyridine 1-oxide takes place by the simultaneous interaction of the nitrous acidium ion with the protonated and the free form of both amines. The nitrous acidium ion shows a distinct discrimination in its reaction with the free amines and this is manifested in a rectilinear relationship between the rate constant for the diazotisation and the Ka values of the amines. Unlike the diazotisation of the free aromatic amines, the diazotisation of the 2- and 4-aminopyridines seems to involve an initial interaction between the nitrosating agent and most probably that part of the heteroaromatic ring system (including the 1 -oxido group when appropriate) which is richer in electrons than the amino-group. The effects of substituents on the rate coefficient for the diazotisation of the protonated 2- and 4-aminopyridines support the view that the diazotisation of these amines involves an initial association of the nitrosating agent with the heteroaromatic ring. There is evidence that the hydroxy-group of the protonated amine 1 -oxide molecules, when in the para-position with respect to the amino-group and therefore not involved in hydrogen bonding with it, accelerates the reaction by providing an additional site for the initial association with the nitrosating agent. pKa Values of 2-amino-5-methyl- and 2-amino-5-chloro-pyridine 1-oxide are recorded.