Triple bond remote

The reaction sequences of Scheme 21 are supported by the following facts (i) the CAD spectrum of the product of H2 loss (40 ) is identical to that of authentic Fe(l-octene-6-yne) (ii) deuterated 2-octynes undergo regiospecific H2 and C2H4 losses, largely involving the triple bond-remote positions C(7) and C(8). ... 

Similarly, 6-mercaptopurine in alkaline medium adds across the triple bond in 3,3,3-trifluoropropyne to form the carbon-sulfur bond to the carbon more remote from the trifluoromethyl group In trifluoromethyl-ferf-butyldiacetylene, the bond is formed to the carbon adjacent to the trifluoromethyl group [5] (equation 6)... 

Participation of more remote triple bonds has also been investigated. Peterson and Kamat (82) have carried out a careful study of the solvolysis in a variety of solvents of 6-heptyn-2-yl tosylate, 69, and 6-octyn-2-yl tosylate, 70. The observed products of solvolysis are given in Schemes IV and V. 

Unlike triple-bond participation, no remote cumulative double-bond (allenic) participation in solvolysis has so far been observed or reported. A summary of triple-bond and allenic participation in solvolysis involving possible vinyl cations is given in Table VI. 

The stannyl cation in zwitterion 80 is only stabilized by side-on coordination with the remote C = C triple bond. The crystal structure of 80 revealed a pyramidalized tin center with the sum of valence angles of 351.1° (see Table XIV). The coordination of the tin atom to the C = C triple bond is unsymmetrical and the SnC distances... 

In 1975 Brown and Yamashita reported that a triple bond in any position of a straight chain hydrocarbon or acetylenic alcohol, when treated with a sufficiently strong base, could be isomerized exclusively to the free terminus of the chain. The "zipper reaction" thus provides a general solution to the problem of remote functionalization of a long hydrocarbon chain. Isomer-izations along chains of thirty carbon atoms have been achieved. 

A triple bond, in stearolic acid, remote from the end group, gives such an increase in attraction for the water, combined with little increase in the lateral adhesion between the chains, that the films are vapour-expanded. This triple bond produces a considerable increase of surface potential. 

Besides activating the triple bond towards Michael addition the electron-withdrawing group (EWG) introduced by Sonogashira coupling can also exert an activation of the remote propargyl position (Scheme 8). This propargyl activation could for... 

The more difficult cross-coupling reaction between Csp -Csp can be accomplished by mixed zincate compounds, prepared by the reaction of diorganozinc derivatives with Me2CuMgCl-MgCl(CN) (equation 59). Substitution reaction at Csp centers are also efficiently catalyzed by Ni salts when the alkyl halide contains a double bond in remote position (Scheme 22). Changing the double bond for a triple bond leads to an intramolecular carbozincation reaction (equation 60). 

Many acetylenic acids have been made by the dehydrohalogenation of the dibromo derivatives of olefinic acids. Aliphatic a,/3-acetylenic acids are often decarboxylated under the conditions of the reaction. However, phenylpropiolic acid, C,HsC = CC0,H, and acetylenedicarboxylic acid, HOaCC=CCO,H, are prepared in this way as well as acids having the triple bond in the / y-, y, S-, and more remote positions in the aliphatic chain. 

Reactions Remote from the Complexed Triple Bond... 

Alkynes carrying unpaired electron centers are classified into three groups depending on in which part of the molecule the unpaired electron resides in a substituent remote from the alkyne moiety, in a transition metal ion Ugated with the alkyne, or a to the C=C triple bond. 

An optimized procedure (in situ) for the oxazaborolidine-catalyzed reduction is disclosed. Several papers describe the access to propargylic alcohols,and it is interesting to note that strong remote steric effects are transmitted across the triple bond. ... 

Alkynes bearing a hydrosilane group at a remote site undergo silylformylation Thus, regio- and stereoselective functionalization of the triple bond is realized. 

The strongly directing carbamate group allows for the presence of remote sty-ryl or phenylethynyl groups during the enantioselective deprotonation step of the substrate. The phenyl group activates the double or triple bond for an intramolecular carbolithiation [109]. Since carbolithiation is the topic of Chapter 9, only few representative ideas and examples are discussed briefly below. 

Isomerization of acetylenic alcohols. In the presence of this base internal triple bonds of acetylenic alcohols migrate to the terminus remote from the —OH group. -Examples ... 

Helal CJ, Magriotis PA, Corey EJ (1996) Direct Catalytic Enantioselective Reduction of Achiral a,p>-Ynones. Strong Remote Steric Effects Across the C-C Triple Bond. J Am Chem Soc 118 10938... 

---