Rhodium-Catalyzed Intramolecular C−H Insertion of α-Aryl-α-diazo Ketones

Abstract

Direct diazo transfer proceeds smoothly with α-aryl ketones. The derived α-aryl-α-diazo ketones cyclize efficiently with Rh catalysis to give the corresponding α-aryl cyclopentanones.

Synthesis of (−)-Hamigeran B

“…In order to develop this approach to cyclopropane construction, two challenges (Scheme 2) had to be overcome 11. The first challenge was to optimize the base, solvent and sulfonyl azide for the diazo transfer reaction on an α-aryl ketone.…”

“…To 300 mL of toluene were added the ketone 19 (10.0 g, 28.2 mmol), DBU (8.6 g, 56.5 mmol) and 2,4,6-triisopropylbenzenesulfonylazide (10.5 g, 33.9 mmol) sequentially at 0 °C 11. The reaction mixture was maintained in darkness and stirred at rt for 4 h. The reaction mixture was directly chromatographed to afford the diazo ketone 11 as a yellow oil (9.66 g, 25.4 mmol, 90% yield).…”

New Syntheses of Diazo Compounds

“…The combination of p ‐acetamidobenzenesulfonyl azide and DBU has emerged as the method of choice for these applications. The combination of a sulfonyl azide and DBU can also be used to prepare α‐aryl‐α‐diazoketones: however, depending on the electronic nature of the aryl substituent, the yield is strongly influenced by the azide, the amount of base, and the solvent 30…”

Neues zur Synthese von Diazoverbindungen

“…Für die Herstellung von a-Aryl-a-diazoketonen lässt sich die Kombination Sulfonylazid/DBU ebenfalls verwenden; in Abhängigkeit von der Art des Arylsubstituenten kann die Ausbeute jedoch stark vom verwendeten Azid, der Basenmenge und dem Solvens abhängen. [30] Andererseits kön-nen Diazomethylketone und a-Diazocarbonsäureester in der Regel nicht durch direkte Diazogruppenübertragung auf einfache enolisierbare Ketone bzw. Carbonsäureester hergestellt werden.…”