Science of Synthesis

Kubik, S., Science of Synthesis, (2010) 41, 514.

Previous summaries of the chemistry of alkenediazonium compounds can be found in several reviews (see Houben–Weyl, Vol. E 15, pp 1101–1128).[‌109‌,‌110‌] The first examples of diazonium compounds of general structure ‌12‌ bearing the diazonium group in a vinylic position were first described in 1963[‌111‌] and 1964.[‌112‌] These compounds exhibit vastly different relative stabilities depending on their structures, ranging from derivatives that can be isolated as salts and stored at room temperature for an extended period of time,[‌109‌,‌110‌] to those that require in situ generation and trapping,[‌113‌,‌114‌] and those that can be generated only at low temperatures in superacids for direct NMR studies.[‌115‌,‌116‌] In general, alkenediazonium compounds are more stable than alkanediazonium compounds because of (i) stabilization by conjugation and (ii) the fact that loss of nitrogen is associated with the unfavorable formation of an unstable vinyl cation ‌13‌. Resonance forms of alkenediazonium compounds are depicted in ‌Scheme 15‌. These structures indicate that a major contribution to stability could come from electron-donating substituents at the 2-position, giving rise to resonance forms ‌14C‌ and ‌14D‌. Indeed, crystal structures of 2,2-diethoxyethenediazonium hexafluoroantimonate and 2,2-dichloroethenediazonium hexafluoroantimonate give evidence for the importance of this effect.[‌117‌,‌118‌] Alternatively, stability of alkanediazonium compounds can also be increased by destabilizing the cation resulting from cleavage of the C—N bond. The latter can be achieved, for example, by introduction of electron-withdrawing substituents such as fluorine or chlorine into the 1-position (R1) or by introduction of the C=C bond into a five- or six-membered ring, which prevents the vinyl cation produced by loss of nitrogen from adopting a linear arrangement. Theoretical calculations on the electron-density distribution and structure of alkenediazonium ions have been performed.[‌119‌–‌121‌]

‌Meeeee 88‌ Meeeeeeee eee Meeeeeeee Meeeeeeeeeeee ee Meeeeeeeeeeeeee Meeeeeeee

Meeeeeee eee eeeee eeeeee eeeeeeeee eeee eee eeeeeeeeeeeee ee eeeeeeeee-eeeeeeeeee eeeeeeeeeeeeeee eeeeeeeee, eee eeeeeee 8-eeeeee-8-(8-eeeeeeeeeee)-8-eeeeeeeeeeeeeeeeeeeeeeeee (‌88‌), eee ee eeeeeeee ee ee eeeeeee eee eeee eee e eeeeeee β-eeeeeeeeeeeee eeeeeeeee, eeeeeeeee eeeeeeeeeeeee ee eeeee eeeeeee ee eeeeeeeeeeee eeeeeee eeee eeee ee eeeee eeeeeeeeee (e.e., ‌88‌, ‌Meeeee 88‌).[‌888‌] Meee, eee eeeeeeeeee ee ‌88‌ ee eeeeeee eeeeeeee ee eee M—M eeee ee eeee eeeeeee eeee eee eeeeee eeeeeeee ee eeeeeeee ee eeeee eeee eeeeeeeeeeeeeee eeee.[‌888‌]

‌Meeeee 88‌ Meeeeeeeeeeee ee ee Meeeeeeeeeeeeee Meeeeeee ee ee Meeeeeee-Meeeeeee Meeeeeeeeee ee eee 8-Meeeeeee[‌888‌]

Meeeeeeee eeeeeeeeeeeee ee eeeeeeeeeeeeeee eeee eeee eeeeeeee-eeeeeeee eeeeeeeeeeee ee eee 8-eeeeeeee eeeeeeeee eee eeee eeeee ee eee M≡M eeee. Me eeeeeeeeeeee eeeeeeeeee eee eeee eeeeee ee eee MM eeeeeeeeeeeeeeeee eeeeeeeeee eeeeeeeeee ee eee eeeee eeeeeeeee eeeeeeeee ee eee eeeeeeeeeeee eeeeeee ee eee eeeeeeeeeeeeeee eee (‌Meeee 8‌).[‌888‌] Meee, eeeeeeeeeeeeeee eeee eeee eeeeee eeeeeeeeeeee ee eee 8-eeeeeeee eeeeeee eee eeeeeee M—M eeeeeeeee eeeeeeeeeee, eeeee eee, eeeeeee, eeeee eeeeeee eeee eee eeee ee eeeeeeee eeeeeeeee eeee (eeeeeeeeeeeeeeee eeeeeeeeeeeeeeeee ν̃: 8888 ee−8).[‌888‌] Meeee ee eeeeeeee eeeeeeeeeeee eeeeeeee eeeeeeee eee eeeeeeeee eeeeeeeee. M eeeeee eeeee ee eeeeeeee eee eeeeee eeeeeeeeeeee eeeee eeeeeeeee eeeeeeee- eee eeeeee-eeeeeee eeeeeeeeeeee (ee eeeeeeee ee ee eeeeeeee eeeeeeeeeee ee eee 8-eeeeeeee) ee ‌88‌ eeeeee eee eeee eeeeeeeeee eeeeee. Mee eeeee eeeeeeeee eeeeeeeee ee ‌88‌ ee eeeeeeeeee ee eeee ee eeeeee eeeeeeeeeeee (ν̃: 8888 ee−8).[‌888‌] Mee eeeeeeeeeeee ee ee eeeeeeeeeeeeeee eee eeeeeeeee ee eee eeeeeeeee ee eeeeeeeeeeeee-eeeeeeeeeee (eeeeeeeeeee)eeeeeeeeee eeeeeeeee ee eee eeeeeeeee ee MM eeee.[‌888‌]

M eeeeeee eeeee eee ee eeeeeeee ee eee 8M MMM eeeeeee ee eeeeeeeeeeeeeee eeee: eee eeeeeeee eee eeeeeeee eeeeeeee ee eeeeeeeeeeee ee eee 8-eeeeeeee, eee eeeeeeee ee eee eeeeeeeee ee e eeeeee ee eee 8-eeeeeeee.[‌888‌] Mee eeee eeeee ee eee M=M eeee ee eeeeee eeeeeeeee-eeeeeeeeee eeeeee eeeeeeeee eeee ee eeeeeee ee ee eeeeee eeee eeee eeeeeeee ee eeeeeeee ee eee eeeeeeeee ee eee MMM eeeeeeeeee.

‌Meeee 8‌ Meeee Meeeeeeee Meeeeeeeeee ee Meeeeeee Meeeeeeeeeeeeee Meeeeeeeeeeeeeeeeeeee[‌888‌,‌888‌,‌888‌]

Meeeeeeeeeeeeee eeee eee eeeeee eeeeeeeeeeeee eeeeeeee. Meee eee eeeeeeeee ee 8-(eeeeeeeeeeee)eeeeee-8-eeeeeeeee eeee, eeeee eeeeeeeeeeeeeeeee ee eeeeeeeeeeeeeeeeeeee eeeee eee eeeeee ee eeeeeeee,[‌888‌,‌888‌] eeee eee eeeeeeee ee eeeeee eeeeeeee. Meeee eeee eeeeeeeeeeeeeeee ee eeee eee eeeeee eee eeee eeeee ee eeeeeeeeeeeeeee eeee eeee eeee eeeeee eeeeeeeeeeee eeeeeee eeeeee eeee ee, eee eeeeeee, eeeeeeeeeeeeeeeeeeee ee eeeeeeeeeeeeeeeeeeee eeee eeee eeeeeeee.

Meee eeeeeeeeeeee eeeee eeee eeeeeeeeeeeeeee eeee ee eeeeee ee eee 8-eeeeeeee (‌Meeeee 88‌). Meeeeeeeeee eeeeeeeeeeeee eeee eeeeee eee eeeeeeeeeeee eeeeeee eeeeeeeeeee ee eeeeeee eeeeeeeeeee ee eeee e eee eeeeeeeeeeeeeee eeeeeeeeee (eee Meeeeee ‌88.8.8.8.8‌). Meeeeeeeeeee eeeeee ee eee eeeeeeeee eeeee eee eeee eeee eeeeeeee ee eeeeeeeee eeee eee eeeee eeeee.[‌88‌]

‌Meeeee 88‌ Meeeeeee ee Meeeeeeee eeeeeee Meeeeeeeeeeeeee Meee eee Meeeeeeeeeee

Meeeeeeeeeeeeee eeee eeee e eeeeeeee ee eee 8-eeeeeeee eee ee eeeeeeeeee eeeeeeeeeeee ee eeee 8-eeeeeeee-8-eeee. Meee eeeeeeee ee eeeeee ee eeeeeee eeeeeeeeeee ee eee 8-eeeeeeee (eee Meeeeee ‌88.8.8.8.8‌). Meeeeeeeee eeee ee eeeeeeee eeeeeeee eeeeeeeeeee eeeeeeee,[‌888‌] eeeee eee eeeeeeeeee ee eeeeeeeee ee eeeee eeeeeee, eeeeeeeeeeee, eeeeeeeeeeeeeeeeeeeeeee, eee eeeee eeeee eeeeeeeeeee (eee Meeeeee ‌88.8.8.8.8‌).

References