Unusual rearrangements of 2-aroylimidoyl-2-phenylethylidene to 2,5-disubstituted oxazoles

Gold-catalyzed formal [4π + 2π]-cycloadditions of propiolate derivatives with unactivated nitriles

“…Such formal cycloadditions are applicable to diverse tert -butyl propiolates and nitriles, yielding useful 6 H -1,3-oxazin-6-ones, which are not readily prepared with current methods. 8 This new finding enables a one-pot gold-catalyzed synthesis of highly substituted pyridines through sequential reactions of tert -butyl propiolates with nitriles, and then with electron-deficient alkynes in the same solvent. The utility of these [4 + 2]-cycloadditions is further expanded with various aldehydes, ketones and 2-phenyloxetane, yielding satisfactory yields of cycloadducts.…”

“…This work provides a new version of tert -butyl propiolates that feature useful four-atom building blocks with polar π-bond motifs such as nitriles, aldehydes and ketones, although their reactions with alkenes were reported to be restrictive. 8 …”

“… 5 In a significant advance, we here report the gold-catalyzed formal hetero-[4π + 2π]-cycloadditions 6 , 7 of various propiolates with nitriles to afford 6 H -1,3-oxazin-6-ones efficiently (eqn (3)). 8 These findings enable the development of new cascade cycloadditions using three π-motifs including propiolates, nitriles and alkynes, yielding highly substituted pyridine derivatives. Notably, 6 H -1,3-oxazin-6-ones are useful intermediates in various organic reactions whereas highly substituted pyridines are important structural cores commonly found in many bioactive molecules (see ESI Fig.…”

Isoxazol-5-ones as Strategic Building Blocks in Organic Synthesis

“…This proved to be of no consequence, as during FS-FVP these substrates decompose via a retro-Michael mechanism to the corresponding 4-alkylideneisoxazol-5-ones 59k and 59l and further heating produces the expected alkynes 60k and 60l, respectively (Scheme 10). 64 Other applications of FVP, developed by Prager and coworkers, allowed the conversion of isoxazol-5-ones to imidazoles, 65 oxazoles, 66 and indoles, pyrroles, or quinolones. 67 The photolysis of isoxazol-5-ones (generally using λ = 300 nm) has been also studied; carbene intermediates were also generated to afford a variety of heterocycles.…”

Flash Vacuum Pyrolysis of 2,5-Diphenyloxazole

“…Though flash-vacuum pyrolyses (FVP) of a few substituted and annulated isoxazoles [4][5][6] as well as of different isoxazolones [7][8][9] were investigated (revealing the preferential fission of the N-O bond, and the extrusion of CO 2 , respectively) reports on the gas-phase chemistry of oxazoles are very scarce. Thus, it has been proved that unsubstituted oxazole radical cation dissociates by elimination of a hydrogen atom [10] whereas 2-phenyl-1,3-oxazol-5(4H)-one thermally eliminates CO 2 [11].…”