Alkyl groups addition reactions

Conjugate Addition of Alkyl Groups Organocopper Reactions... 

Addition of Fluoride and Alkyl Groups (Fluoroalkylation Reactions)... 

ALKYLATION. Addition of an alkyl group. These reactions are important throughout synthetic organic chemistry for example, in the production of gasoline with high antiknock ratings for automobiles or for use in aircraft. 

The rate of an acid-cataly2ed hydration is very much dependent on the structure of the starting alkene. Compare the relative rates of the following three reactions, and analyze the effects of an alkyl substituent on the relative rate of each reaction. With each additional alkyl group, the reaction rate increases by many orders of magnitude. Also take special notice of where the OH is placed in each of the cases above at the more substitutedposition. 

Although the intermediacy of unstable N-unsubstituted imines has been proposed during the acid- or base-catalysed decomposition of oxaziridines bearing an a-hydrogen atom on the iV-alkyl group, the reaction conditions employed have not permitted their detection. A recent report has now shown that addition of D ABCO or DBN to solutions of oxaziridines (37) gives aldimines (38) which could be isolated or detected, depending upon the nature of R. ... 

When R is a simple alkyl group, addition of the phosphonate carbanion to the carbonyl compound occurs but the intermediate does not undergo elimination. Since the reaction sequence results in the conversion of an aldehyde or ketone to an alkene, as does the Wittig reaction, but works well when electron-withdrawing... 

With respect to the application of tartaric acid-derived PTCs [22,23] for natural product synthesis, the work of Shibasaki s group should be highlighted herein. Using his powerful bidentate TaDiAS PTCs, asymmetric phase-transfer-catalyzed alkylations, Michael addition reactions, and Mannich-type reactions have been systematically carried out. 

The introduction of additional alkyl groups mostly involves the formation of a bond between a carbanion and a carbon attached to a suitable leaving group. S,.,2-reactions prevail, although radical mechanisms are also possible, especially if organometallic compounds are involved. Since many carbanions and radicals are easily oxidized by oxygen, working under inert gas is advised, until it has been shown for each specific reaction that air has no harmful effect on yields. 

Out first example is 2-hydroxy-2-methyl-3-octanone. 3-Octanone can be purchased, but it would be difficult to differentiate the two activated methylene groups in alkylation and oxidation reactions. Usual syntheses of acyloins are based upon addition of terminal alkynes to ketones (disconnection 1 see p. 52). For syntheses of unsymmetrical 1,2-difunctional compounds it is often advisable to look also for reactive starting materials, which do already contain the right substitution pattern. In the present case it turns out that 3-hydroxy-3-methyl-2-butanone is an inexpensive commercial product. This molecule dictates disconnection 3. Another practical synthesis starts with acetone cyanohydrin and pentylmagnesium bromide (disconnection 2). Many 1,2-difunctional compounds are accessible via oxidation of C—C multiple bonds. In this case the target molecule may be obtained by simple permanganate oxidation of 2-methyl-2-octene, which may be synthesized by Wittig reaction (disconnection 1). 

Classical syntheses of steroids consist of the stepwise formation of the four rings with or without angular alkyl groups and the final construction of the C-17 side-chain. The most common reactions have been described in chapter 1, e.g. Diels-AIder (p. 85) and Michael additions (p. 

Table 6 3 shows that the effect of substituents on the rate of addition of bromine to alkenes is substantial and consistent with a rate determining step m which electrons flow from the alkene to the halogen Alkyl groups on the carbon-carbon double bond release electrons stabilize the transition state for bromonium ion formation and increase the reaction rate... 

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