1.2- dihalogenoacetylenes

Rather than fearing and consequently avoiding the high reactivity and often explosive character of 1-halogeno- and 1,2-dihalogenoacetylenes, there are more and more examples in the modern literature which deliberately set out to use this reactivity imaginatively for synthetic purposes. 

The high propensity for addition to 1-halogeno- and 1,2-dihalogenoacetylenes has often been noted [4, 60], and 100 is no exception in this respect [93]. With secondary amines, the... 

As in the case of the cyanoacetylenes (see above), we intend to discuss in this section the preparation of the ethynologs of the parent systems, i.e., the extended versions of the simple halogeno- (92-95) and dihalogenoacetylenes (96-105). Although a sizeable number of these molecules have been prepared, their chemistry - because of their very high reactivity and the difficulties involved in handling them (see below) - remains largely unexplored. 

Among the other dihalogenoacetylenes listed in Section 2.3.2.11,2-diodoacetylene (105) has been used most often in preparative and mechanistic work, which is not surprising considering the relative stability of this compound and its ease of preparation. In a remarkable displacement reaction, 105 reacts with Mn(CO)5" to afford the bis-metal(carbonyl complex) 155 whereas with other metal carbonyls such as rhenium pentacarbonyl, a formal abstraction leading to 156 and 157 is observed [101] (Scheme 2-16). 

Attempts to obtain the hitherto unknown acetylenes BrCiCF and ICICF were not successful " the route chosen was a general one which had been successfully applied to the synthesis of dihalogenoacetylenes not containing fluorine ... 

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