Protophilic attack

The hydrohalogenation of phenyl(3-methyl-l,2-butadienyl) phosphinic esters involved protophilic attack of the reagent, followed by heterocyclization of the allenephosphonate system (Scheme 40) [103, 104],... 

When the metalation of 2-fluoropyridine (8) was carried out at lower temperatures (-60°C), aside from the product of addition 13, evidence for the DoM product 12 was obtained by a TMSC1 quench experiment (Scheme 4). Complete chemospecificity was achieved only with the more selective LDA base at -75°C. [81JOC4494,81JOM(215)139]. Whereas the soft character of n-BuLi favors nucleophilic reactivity, the hard LDA leads to preferential protophilic attack. The stronger kinetic basicity... 

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