Olefins, atom addition

Since electron-donating substituents at the phosphorus atom favor addition reactions over olefination reactions, addition of 9 to aldehydes leads to the exclusive formation of the silyl-pro-tected allylic alcohols 10. No reaction products arising from Wittig alkenylation could be detected. The ylides (R,S)-9 and (S.S)-9 and their enantiomers were prepared from the corresponding optically pure l-[2-(diphenylphosphino)ferrocenyl]-A,A -dimethylethanamine diastereomers 7 via the phosphonium salts 8. 

Thus, the rule of Keulemans (49), that a-quaternary carbon formyl compounds are not formed, was followed. The olefin isomerized to allow formyl attachment to a primary carbon atom. Addition of phosphine, which decreases isomerization, resulted in no reaction. 

Frjedel-Crafts Reaction. Any organic reaction brought about by the catalytic action of anhydrous aluminum chloride or related, so-called Lewis acid type catalysts. Discovered in 1877 by C. Friedel and J.M. Crafts, who later uncovered most of the types of reaction such as substitution, isomerization, elimination, cracking, olefin polymerization, addition, etc. Commonly used to displace an aromatic hydrogen atom with an alkyl, aryl or acyl chain... 

Rabinovitch et al. (85) studied the reaction of H atoms with trans-ethylene-d2 as a function of ethylene pressure in the temperature range — 78 to 160°C. They were able to account for all secondary reactions of the hot ethyl radicals and to determine the rates of their decomposition (relative to stablization). Simultaneously they calculated the theoretical rates on the basis of the Rice-Ramsperger-Kassel theory of uni-molecular reactions, using expressions derived by Marcus (71), and found a reasonable agreement with the experimental values. Similar satisfactory agreements had been found previously by Rabinovitch and Die-sen (84) for hot sec-butyl radicals. Extensive studies of hot radicals produced by H or D atom additions to various olefins have been carried... 

There can be little doubt that the summarized work of Dainton and and his collaborators has pointed to a new important feature of the reactions of chlorine atoms with olefins. The incorporation of the reactions of hot radicals into the general olefin photochlorination mechanism brings these reactions into closer analogy with the other atomic addition reactions discussed in this article. It may be anticipated that further work on such effects will be forthcoming. It would be in particular desirable to obtain further verification of the postulated collisional deactivation of the excited AClf radicals by carrying out... 

Reactions of the recoil C1] with several olefins have been studied, including ethylene, propylene, cyclopentene, and cfs-butene-2, as well as with several paraffins. The type of products observed indicated the existence of several general modes of interaction, such as CH bond insertion, interactions with CC double bonds, formation of methylene-C11. The most important single product in all systems is acetylene, presumably formed by CH insertion and subsequent decomposition of the intermediate. Direct interaction with double bonds is shown by the fact that, for example, in the case of propylene, yields of stable carbon atom addition products were significantly higher than in the case of propane. The same was true for ethylene and ethane. 

Relative Rate Constants for Oxygon and Sulfur Atom Addition Compared with the Quenching Cross Sections of Olefins for Hg GOP,) Atoms... 

As described in the experimental section single-step radical-molecule reactions can be studied in isolation and in a very direct way by using the rotating cryostat. The identity of the initial radical is known and the product radical can usually be identified unambiguously by e.s.r. Also the relative amounts of the primary and product radicals can be obtained by analysis of the composite e.s.r. spectrum and thus the extent of reaction can be determined directly. When there is more than one site in a molecule at which reaction can occui, the resulting e.s.r. spectrum, which consists of the spectra of the different product radicals, can often be analysed to give the relative degree of attack at the different sites in the molecule (e.g. as for H-atom addition to an unsymmetric olefin). 

Methyltrioxorhenium has been found to be a universal catalyst for a number of [2-1-1] cycloaddition reactions, including nitrene, carbene, or oxo-atom addition to olefins <2001GC235>. Typically, to increase the chemical yield of the reaction, at least 5 equiv of an olefin is required. As with most nitrene transfer reactions, simple cyclic olefins such as cyclohexene produce a low chemical yield of aziridine. The authors assume that the intermediate of the reaction is a reactive rhenoxaziridine intermediate. 1,2-Dihydronaphthalene provides aziridine 28 in 43% chemical yield under these reaction conditions (Equation 11). 

Molecular and Atomic Addition of Hydrogen. It is generally accepted that the reaction of an adsorbed alkyne (see Section III, B, 1 for notation) with two adsorbed hydrogen atoms in two consecutive steps yields an olefin in the cis-configuration. The hydrogen atoms, in this case, react by addition from below the axis of unsaturation ... 

Hydroboration provides a convenient and direct access to organoboranes from olefins via addition across the carbon-carbon double bond. A discussion of the hydroboration reaction and of the synthesis of enantiomerically pure organoborane intermediates by asymmetric hydroboration of proslereogenic olefins is given in Section D.2.5.2.1. The present section deals with subsequent stereoselective carbon-carbon bond formation from enantiomerically pure or enriched organoboranes which bear the boron atom at the stereogenic center1-8. 

The olefins, and in particular ethylene where the ethyl radical formed by hydrogen atom addition... 

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