How Nucleophilic Are Diazo Compounds?

Abstract

The kinetics of the reactions of benzhydryl cations with eight diazo compounds 1 a-g were investigated photometrically in dichloromethane. The nucleophilicity parameters N and slope parameters s of these diazo compounds were derived from the equation log k (20 degrees C)=s (E+N) and compared with the nucleophilicities of other pi systems (alkenes, arenes, silyl enol ethers, silyl ketene acetals). It is shown that the nucleophilic reactivities of diazo compounds cover more than ten orders of magnitude, being comparable to that of styrene on the low reactivity end and to that of enamines on the high reactivity end. The rate-determining step of these reactions is the electrophilic attack at the diazo-carbon atom to yield diazonium ions, which rapidly lose nitrogen.

1,3-Dipolar cycloadditions of diphenyldiazomethane to thioketones: Rate measurements disclose thiones to be superdipolarophiles

“…The bis( p-dimethylamino)benzhydryl cation reacts with diazomethane 1.3 × 10 4 times faster than with diphenyldiazomethane 7. The nucleophilicity parameter N of 7 has been determined [38], but the electrophilicity E of thiobenzophenone is unknown.…”

The Reactivity–Selectivity Principle: An Imperishable Myth in Organic Chemistry

“…Chemie alkanes, [62] ketene acetals, [52,63] enol ethers, [52,64] water, [65] transition metal p-complexes, [52,66] alkenes, [52] hydride donors, [49,67] and arenes [52,68] with benzhydrylium ions follow linear correlations with the electrophilicity parameter E. In some cases it has been shown that these correlation lines bend for k > 10 8 m À1 s À1 and asymptotically approach the diffusion Figure 8. Rate constants for the reactions of carbenium ions with allylsilanes.…”

Towards a General Scale of Nucleophilicity?

“…[8,9] The most extensive nucleophilicity scale, [10,11] presently available, has been derived from the rate constants of the reactions of benzhydrylium ions with alkenes, arenes, enol ethers, ketene acetals, [12] enamines, [13] allyl element compounds, [14] transition-metal p-complexes, [15] diazoalkanes, [16] and delocalized carbanions [17][18][19] (p-nucleophiles), amines, [20] alcohols, [21] alkoxides, [22] phosphanes, [23] inorganic anions [24][25][26][27] (n-nucleophiles), and a variety of hydrides [28][29][30][31] (s-nucleophiles); these rate constants were subjected to a least-squares minimization on the basis of Equation (3) [10,11] in which k is the second-order rate constant at 20 8C and E is a nucleophileindependent electrophilicity parameter.…”