α-Diazo-λ³-iodanes and α-diazo sulfonium salts: the umpolung of diazo compounds

Abstract

This article reviews the strategies available to achieve the umpolung of diazocompounds and the synthetic applications of such compounds.

Electron Donor–Acceptor Complex Enabled Radical Cyclization of α-Diazodifluoroethyl Sulfonium Salt with Unactivated Alkynes

“…The obtained α-diazodifluoroethyl sulfonium salt was a yellow solid under ambient conditions and was successfully subjected to single-crystal X-ray diffraction analysis. The lengths of several key chemical bonds were measured to be 1.736 Å for S(2)–C, 1.333 Å for C–N, and 1.113 Å for N–N, which are identical to those of the reported α-diazo sulfonium compounds . Interestingly, several noncovalent interactions, including C–H···π and π···π interactions, were observed between the dibenzothiophene moiety and the phenyl group (C–H–benzene distance was calculated to be 3.05 Å, and the centroid–centroid distance of two phenyl rings was calculated to be 4.38 Å), possibly contributing to the stabilization of this reagent …”

“…Recently, the exploration of diazo compounds as a source of radical intermediates under visible light irradiation conditions has gained significant attention . In particular, the groups of Alcarazo and Wang have disclosed the synthesis of α-diazo sulfonium salts and demonstrated their unique radical reactivity under photoredox catalysis conditions . Very recently, Zhao, Yuan and co-workers reported the radical [3 + 2] cycloaddition reaction of α-diazosulfonium triflates with alkynes for the synthesis of 3,5-disubstituted-1 H -pyrazoles under blue light conditions, but the dipolarophile scope is restricted to aromatic alkynes (Scheme b) .…”

Trifluoromethyl Rhodium‐Carbynoid in [2+1+2] Cycloadditions

“…Very recently, the multifunctionalizations of RC + =M (R=CO 2 R’, COR’; M=Rh, Cu) were independently investigated by the groups of Huang [11] and Hu [12] . Although remarkable advancements have been achieved using RO 2 CC + =Rh, [9–13] trifluoromethyl metal‐carbynoid (CF 3 C + =M) has not yet been explored for catalytic reactions, which remains challenging owing to the strong electron‐withdrawing ability of the trifluoromethyl (−CF 3 ) group, thus leading to high instability of the carbocation intermediate. Therefore, we hypothesized if the untapped CF 3 C + =M equivalent could be generated via successive denitrogenation and heterolysis of the C( sp 2 )−( L ) bond of α‐diazotrifluoroethyl reagents using a Rh catalyst, and further applied to organofluorine chemistry, especially for constructing CF 3 ‐containing heterocycles.…”

Reactivity of α-diazo sulfonium salts: rhodium-catalysed ring expansion of indenes to naphthalenes

“…Recently, Suero and co-workers reported the Rh-catalysed formation of cyclopropyl-I( iii ) intermediates A by reaction of α-diazoiodonium salts with olefins. 8,9 Such species smoothly evolve, even at temperatures as low as −50 °C, to synthetically useful allylic cations B via scission of their distal C–C bond with concomitant elimination of the iodine moiety (Scheme 1A). Due to this intrinsic reactivity, cyclopropyl-substituted iodonium salts have eluded systematic isolation and, in fact, compound C is the only member of the series that has been characterized (Scheme 1B).…”