Followed by HBr Elimination

Method E Treatment of Cyclic Tin Compounds with PBr3 Followed by HBr Elimination 

The direct synthesis of 1.1-substituted X -phosphorins requires many tedious steps (see p. 76). Cleavage of the 1.1-substituents is possible in some cases (see p. 90), but on the whole this method has no preparative value. 

On the other hand, X -phosphorins can easily be converted to 1.1-hetero-X -phosphorins which can be reconverted by cleaving the 1.1-substituents to the X -phosphorins (see p. 88). The value of this procedure lies in the fact that the phosphorus of the X -phosphorins can be protected by the 1.1-hetero groups. 

Functional groups can than be introduced or altered. The new X -phosphorin-com-pound is then reconverted to a X -phosphorin which cannot be synthesized in any other way. 

Method G 4.4 -Bis-X -phosphorins from Thermolysis of 1.4-Dihydro-X -phosphorins 

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The vinyl derivative was converted to ethynyl-CTM by reaction with bromine followed by HBr elimination. The double bond of vinyl-CTM turned out to be much less active than that in the ferrocene analog as regards electrophilic addition. Also, the stabilization of an a-carbonium center, the phenomenon characteristic of ferrocenyl cation, was not found in the manganese compound (379). 

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