Structure and Spectroscopic Properties

Transition‐Metal‐Free C(sp2)–C(sp2) Cross‐Coupling of Diazo Quinones with Catechol Boronic Esters

“…Changing the substituent on the diazo quinone or the phenyl group of the aryl boronic ester from CH 3 to an electron-withdrawing CO 2 Me group facilitated the reaction, but the difference was approximately 2-fold, as depicted in Schemes 4a and 4b.T hese experiments are consistent with the mechanism shown in Figure 2, in which electron-withdrawing group on diazo quinone or boronic ester will facilitate N 2 extrusion of diazo quinone to form quinone carbene [17] or trapping of singlet carbene intermediate, respectively.F or the reaction of diazo quinone 1a and aryl boronic ester 2g-1,byproduct phenol 6 was generated in 7% yield (Scheme 4c), indicative of the involvement of the carbene intermediate. [18] DFT calculations were employed to further explore the reaction mechanism using diazo quinone 1k and aryl boronic ester 2g-1 as example.W ef irst examined the commonly proposed pathway that involves nucleophilic attack of the boronic ester by the diazo quinone and subsequent 1,2rearrangement.…”

Aryl Trialkylsilyl Ketenes: Acid‐Catalyzed Synthesis from 1‐Aryl‐2‐diazo‐2‐trialkylsilylethanones and Their Conversion into 3‐Silyl‐1‐silyloxyallenes

“…Acceleration of the Wolff rearrangement in the presence of protic nucleophiles, such as alcohols and water at neutral pH, has been observed before for other diazo ketones, for example, 1-aryl-2-diazo-2-phenyl-1-ethanones (substituted azibenzils); in contrast, solvolysis of azibenzils by aqueous acids affords only low yields of the ketene-derived diarylacetic acids. [12,13] However, the influence of protons or protic nucleophiles on the decomposition pathways of α-diazo ketones has been a subject of some discussion. On the basis of these investigations and other knowledge of the behavior of α-diazo ketones toward acids, [12] one may assume that silyldiazo ketone 3 is initially O protonated by HOTf to form a β-enoldiazonium ion, which is then transformed into a vinyl cation by loss of N 2 ; 1,2-aryl shift and proton loss would finally yield silyl ketene 3.…”

“…[12,13] However, the influence of protons or protic nucleophiles on the decomposition pathways of α-diazo ketones has been a subject of some discussion. On the basis of these investigations and other knowledge of the behavior of α-diazo ketones toward acids, [12] one may assume that silyldiazo ketone 3 is initially O protonated by HOTf to form a β-enoldiazonium ion, which is then transformed into a vinyl cation by loss of N 2 ; 1,2-aryl shift and proton loss would finally yield silyl ketene 3. In contrast, C protonation of 3 and counterion-assisted desilylation would explain the formation of small amounts of diazo ketones 1.…”

Trimethylsilyldiazomethane Disassembly at a Three-Fold Symmetric Iron Site

“…More exotically, the metal can function as a substituent on the diazoalkane in the form of a C-bound diazoalkane complex. 2,3 We (and others) have shown the utility of rigid, strongly donating tris(carbene)borate ligands for the isolation of late transition metal complexes bearing metal−ligand multiple bonds. 2−5 By stabilizing a 3-fold symmetric environment at a four-coordinate metal center, these ligands create a d-orbital manifold that diminishes destabilizing σ* and π* interactions with the multiply bonded ligand.…”

“…However, this same diazo group may also be associated with undesired complications, including two commonly observed coordination modes: “end-on” in which the metal is σ-bonded through the terminal nitrogen atom of the diazoalkane, and “side-on” via the diazoalkane π-system. More exotically, the metal can function as a substituent on the diazoalkane in the form of a C -bound diazoalkane complex. , …”