Diynes reactions

The preparation of condensed rhodacyclopentadienes via the diyne reaction, and examples of their use in heterocyclic synthesis have been described earlier (see Schemes 79 and 86 in Sections IV,B,5 and IV,C,2). An example showing the application of this approach to the synthesis of a condensed triazole is shown in Scheme 127.192... 

The diyne reaction has been used extensively by Muller et al. in heterocyclic synthesis (see for example Scheme 86 in Section IV,C,2) a process using a diyne substrate and leading to the formation of an azuleno[l,2-d]-dibenzo[b,/]silepin is shown in Scheme 172.243fl... 

Cyclic addition reactions of 16a with diynes or cyanamide are interpreted as being initiated by an electrophilic attack of the cyanamide or the terminal carbon atom of a C=C bond. Both result in ring expansion and the formation of 2,4-As,As-diphosphapyridine 39 <1998ZNB443> or l,3-A5,A5-diphosphabenzenes 40, respectively (Scheme 10). The diyne reaction is not limited to conjugated systems. 1,5-Hexadiyne and 1,7-octadiyne can be used as well <1997JOM(529)223>. 

The ene-diyne reaction (Bergman cyclization) chemistry described below is not part of the biologically related radical reactions. However, after the successive discovery of... 

Buta-l,3-diyne, reaction with ethylenediamine, 56, 9 Butane-2,3-dione, perlluoro-, heterocycles from, 59, 17... 

The diyne reactions of 1,4-, 1,5-, 1,6-, and 1,7-diynes via transition metal complexes are useful for the synthesis of new cyclic compounds (Muller, 1974 Wagner and Meier, 1974, 1975). t-C5H5Co(CO)2 reacts catalytically with linear l,m-diacetylenes (XXXVIII) to give trimers (XXXIX), formation of which involves the interaction of six acetylene functions (Vollhardt and Bergman, 1974). 

Mixed cyclizations also have been achieved via the diyne reaction [Eq. (82)]. Most of the diynes employed thus far have been symmetrical, leading, therefore, to symmetrical rhodacycles. A few representative examples are provided below. An interesting variation is the addition of strained... 

The terminal diyne 320 is prepared by coupling of the zinc acetylide 318 with /rfln.s-l-iodo-2-chloroethylenc (319), followed by elimination of HCI with sodium amide[231]. Similarly, terminal di- and triynes are prepared by using cw-l,2-dichloroethylene[232]. The 1-alkenyl or l-aryl-2-(perefluoroalkyl) acetylene 321 is prepared by the reaction of a zinc acetylide with halides[233]. 

The alkynyl iodide 359 undergoes cross-coupling with a terminal alkyne to give the 1,3-diyne 360[264]. No homocoupling product is formed. This reaction offers a good synthetic method for unsymmetrical 1,3-diynes. 

In the case of the reaction between 2-diazopropane and diphenyldiacetylene, the reverse (as compared with other diynes) orientation of addition of the first molecule of the diazo compound with a predominant formation of 4-phenylethynylpyrazole is observed. Therefore, it is noteworthy that whereas the regioselectivity of the addition of diazoalkanes to alkenes is well studied audits products have, as a rule, the structure been predicted with respect to electron effects, the problem of orientation... 

It was found [99JCS(PI )3713] that, in all cases, the formation of the deiodinated products 38 and 39 was accompanied by formation of the diynes 40 which were isolated in 60-90% yield. The authors believed that the mechanism of deiodination may be represented as an interaction ofbis(triphenylphosphine)phenylethynyl-palladium(II) hydride with the 4-iodopyrazole, giving rise to the bisftriphenylphos-phine)phenylethynyl palladium(II) iodide complex which, due to the reductive elimination of 1 -iodoalkyne and subsequent addition of alk-1 -yne, converts into the initial palladium complex. Furthermore, the interaction of 1-iodoalkynes with the initial alkyne in the presence of Cul and EtsN (the Cadiot-Chodkiewicz reaction) results in the formation of the observed disubstituted butadiynes 40 (Scheme 51). 

It is known that diacetylenes (in Favorsky s reaction, for example) are 1000-fold more active than monoacetylenes. It is of interest to consider how the accumulation of triple bonds will affect the compound acidity. However, in the literature there are no data on the CH acidity of diacetylenic compounds. We were the first to estimate the p/ifa of a monosubstituted diacetylene, 4-butadiynyl-l,3,5-trimethylpyrazole, to be about 24-26 log units. Unfortunately, the authors (83IZV466) have failed to determine the acidity of the diyne more accurately owing to the side processes of remetallization that complicate control over reaction. 

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