Retracted: Palladium‐Catalyzed Decarboxylative Selective Acylation of 4H‐Benzo[d][1,3]oxazin‐4‐one Derivatives with α‐Oxo Carboxylic acids via Preferential Cyclic Imine‐N‐Directed Aryl C−H Activation

Abstract

Theb enzoxazine scaffolds are of much interesta st hey are found in al arge array of natural productsa nd pharmaceutical drugsw ith diverse activities.W eh aved eveloped ap alladium-catalyzed decarboxylative selectivem ono-and bis-acylation of 4H-benzo[d][1,3]oxazin-4-oned erivatives with a-oxo carboxylic acids via preferential cyclic imine-N-directed C À Ha ctivation.2 -Aryl-4H-benzo[d] [1,3]oxazin-4-one was acylated with av arietyo fs ubstitutedp henylglyoxylic acids to produce the corresponding products. It was observed that electron-donating groups (CH 3 ,O CH 3 )a ta ny position of the aromatic ring of phenylglyoxylic acid provided good to excellent yields,w hereasp henylglyoxylica cids containing electron-withdrawing groups (COCH 3 ,C N, NO 2 )g avet he productsi nm oderate yields.I nterest-ingly when the reactionw as performed with silver triflate (AgOTf) in place of silver nitrate (AgNO 3 ) in the presence of 4e quivalents of glyoxylic acid, the bis-acylated product was obtained together with as mall amount of mono-acylated product. This is the first report of acylation of 2-aryl-4H-benzo[d] [1,3]oxazin-4-ones via C À Ha ctivation. Then otable featureso ft his reactiona re acylation with more challenging heteroarene-oxo carboxylic acids and alkyl oxo carboxylic acids.T his new protocolp rovides an easy ande fficient access to av ariety of oacyl-4H-benzo[d][1,3]oxazin-4-one derivatives which are of pharmaceutical importance. Figure1.Af ew biologically active molecules containing the 4H-benzo[d][1,3]oxazin-4-onemoiety. Scheme2.C À Ha cylation of benzoxazine-4-ones with heteroarylglyoxylic acids. 286 asc.wiley-vch.de 2 016 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Adv.Synth. Catal. 2016, 358,283 -295 FULL PAPERS Biju Majhi et al. Scheme 3. Pd-catalyzedC À Ha cylationo f2 -phenyl-4Hbenzo[d][1,3]oxazin-4-one with alkyl a-oxo carboxylic acids. Scheme 4. C À HAcylation of meta-substituted 2-aryl-4H-benzo[d][1,3]oxazin-4-ones.

Palladium‐Catalyzed Decarboxylative Synthesis of 5H‐Benzo[4,5][1,3]oxazino[2,3‐a]isoindole‐5,11(6aH)‐Diones using 2‐Phenyl‐4H‐Benzo[d][1,3]oxazin‐4‐Ones and α‐Oxo Carboxylic Acids

“…[14] In continuation of our work [11] and to explore the expedient behavior of α-oxo carboxylic acids for the synthesis of isoindolinones, reaction between 2phenyl-4H-benzo[d] [1,3]oxazin-4-one (1 a) employing α-oxo carboxylic acid (2 a) was examined. [15] On the contrary, with the same substrates and under identical reaction conditions, we obtained 3 a in 55% yield [Scheme 1(iv), Table 1, entry 2]. However, to our surprise B C Ranu and his group have reported the formation of the acylated product 4 [Scheme 1(iii)] with the same reaction substrates.…”

“…However, to our surprise B C Ranu and his group have reported the formation of the acylated product 4 [Scheme 1(iii)] with the same reaction substrates. [15] On the contrary, with the same substrates and under identical reaction conditions, we obtained 3 a in 55% yield [Scheme 1(iv), Table 1, entry 2].…”

Radical‐Induced, Palladium‐Catalyzed C–H Activation: An Approach to Functionalize 4H‐Benzo[d][1,3]oxazin‐4‐one Derivatives by Using Toluenes, Aldehydes, and Benzyl Alcohols

“…Under these conditions, none of the desired product was observed, which clearly demonstrates that the process occurs through a free radical pathway. When the reaction between 2‐phenyl‐4 H ‐benzo[ d ][1,3]oxazin‐4‐one ( 1a ) and toluene ( 2a ) was carried out at 80 °C, compound 10 was obtained after 15 min (Scheme d) and then converted into 3a upon further continuation of the process. To ascertain whether the product formation involves the migration of the phenyl ring and proceeds through the formation of compound 10 , we treated 10 with TBHP at 120 °C for 18 h. The reaction yielded product 3a (Scheme e), which supported our hypothesis.…”

“…On the basis of results from the above control experiments and reports, a plausible mechanism has been proposed (Scheme ). We believe that initially complex 11 and AcOH are formed by the ortho ‐palladation of 1a with Pd(OAc) 2 .…”

“…Although the synthesis of 4 H ‐benzo[ d ][1,3]oxazin‐4‐one and its derivatives have received significant attention, a simple and general route for the direct functionalization of 4 H ‐benzo[ d ][1,3]oxazin‐4‐one is still unknown. In this regard, Majhi et al recently reported the first regioselective acylation of 4 H ‐benzo[ d ][1,3]oxazin‐4‐one derivatives by using α‐oxo carboxylic acids in a Pd‐catalyzed cyclic imine‐ N ‐directed C–H activation approach . Although this group developed a strategy for the direct functionalization of 4 H ‐benzo[ d ][1,3]oxazin‐4‐ones, the use of an additional AgNO 3 cocatalyst, its low atom economy, and limited substrate scope are drawbacks of this protocol.…”