Using acetylenic reactivity nucleophilic substitution with metal acetylides and related reactions

1 Using Acetylenic Reactivity Nucleophilic Substitution with Metal Acetylides and Related Reactions 

This method has been used for the synthesis of a series of skipped cyclic ene- and diene-diynes [5]. Remarkably high yields are obtained in some cases even for strained compounds, e.g., 4,9-diisopropylidene-l,6-cyclodecadiyne (6) can be obtained in yield by this simple cyclization reaction. The power of this method is further demonstrated by the remarkable synthesis of a tetrasilacyclohexyne (9) by Barton et al. [Eq. (1)] [6]. 

Grignard derivatives of acetylenes have also been used for ring-closure reactions, as is illustrated by the preparation of l,6-dioxa-3,8-cyclodecadiyne (12) from bis(bromomagne-sium)acetylene (11) and di(chloromethyl)ether (10) [Eq. (2)] [7], 

In cases where stable carbocations can be generated, e.g., tertiary propargylic cations, the rather low nucleophilicity of silylated terminal alkynes is still sufHcient for a coupling reaction. Ring closures have been carried out in this fashion to give the permethylated pericyclynes, which are discussed by L. T. Scott and M. J. Cooney in Chapter 9 of this monograph [8]. 

Although copper acetylides seem to be able to perform a nucleophilic substitution reaction at the sp-carbon atom of a bromo- or iodoacetylene (Cadiot-Chodkievicz reaction), this reaction has only rarely been used for the preparation of cyclic 1,3-diacetylenes. Copper-mediated oxidative coupling reactions (Glaser, Hay and Eglinton coupling) are more popular in this area and have attracted much attention in the construction of carbon-rich cyclic and polycyclic systems (see Chapter 13). One of the earliest carbon-rich systems of this type was the CzoHg system 19 [11,16] [Eq. (5)]. 

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