Zipper reactions

Iterative trapping of the alkylpalladium species with tethered olefins is also possible, which allows tandem cycloisomerizations and zipper reactions to take place. Thus, depending upon the juxtaposition of the unsaturated bonds, Trost achieved highly atom-economical syntheses of triquinanes, propellanes (264) from the ynediene 263, and polyspiranes (Scheme 67).261... 

Another practically promising example of intermolecular anion-radical cyclization is a zipper reaction of cyclic o-ethynylbenzenes (Bradshaw et al. 1994 Scheme 7.34). 

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. 

Figure 2.8. Some examples of covalent self-assembly. Note "zipper reaction (bottom).

Zinc, chloro(2-methylphenyl)-, (84109-17-1), 66, 74 Zipper reaction, alkyne Isomerization, 66, 129... 

Steps in denaturation and renaturation of a DNA duplex. In step l the temperature is raised to the point where the two strands of the duplex separate. If denatured DNA is slowly cooled, the events depicted as steps 2 and 3 follow. In step 2 a second-order reaction occurs in which two complementary strands of DNA must collide and form interstrand hydrogen bonds over a limited region. Step 3 is a first-order reaction in which additional hydrogen bonds form between the complementary strands that are partially hydrogen-bonded (zippering). Once complementary strands are partially bonded, the zippering reaction occurs rapidly. In the overall process, step 2 is rate-limiting. 

Palladium(0)-catalysed coupling of non-conjugated dienes, aryl iodides and stabilized carbon nucleophiles has been developed468. An incredibly high yield (86%) of pentacycle 343 has been obtained from a Pd(0)-catalysed zipper reaction of acetylenic pentaene 342. The reaction is triggered off by a Pd-catalysed cyclization of acetylenic bond and the first olefinic bond469. 

Polyolefin cyclization.1 This Pd(0) catalyst in combination with a phosphine ligand and acetic acid effects cyclization of polyunsaturated substrates to polycyclic products in one step (zipper reaction). However, a triple bond is required for initiation. This polyolefin cyclization has been used to prepare tetra- and pentaspirocycles, as a mixture of only two stereoisomers. 

DMSO with Nal catalysis (Sonnet and Heath, 1980), by bromination of a terminal alkene followed by double elimination of HBr (Hoye el al., 1999), or by isomerization of an internal alkyne with the acetylene zipper reaction (Abrams, 1984). 

The acetylene zipper reaction is the shifting of a triple bond in any position of a straight chain internal alkyne to the terminus of the chain in the presence of a very strong base. This multipositional isomerization of the triple bond is especially interesting when applied to acetylenic alcohols as a route to long chain structures with chemically differentiated functionality. 

It was proposed very early in the history of PVC that HCl was lost primarily from positions where the chlorine atom was especially labile because of its location in an allylie position relative to the double bond. Such structures result from the loss of HCl which creates a double bond and thereby makes the adjacent chlorine atom labile. Subsequent loss of HCl appears to be catalyzed by HCl itself and is described as autocatalytic and produces alternate double bonds. Thus, a "zipper" reaction occurs as shown in Figure 22. 

Scheme 9 outlines the synthesis of the (2S, 3R, 4R.5S, 14S)-isomer 57. Cleavage of 54 with the acetylide derived from 55 yielded 58, which was subjected to the acetylene-zipper reaction to give the (9R)-terminal acetylene... 

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