Intramolecular oxyacetoxylation of N-allylamides: an expeditious synthesis of oxazolines and oxazines by using a PhI(OAc)₂/hydrogen fluoride–pyridine system

Abstract

The synthesis of oxazolines and oxazines from N-allylamides was accomplished via an unprecedented reaction set. This reaction involved an intramolecular cyclization of N-allylamides resulting from nucleophilic attack of the allylamine on the benzoxazin-4-one. Unlike the previous literature, the isolable N-allylamide could readily be subjected to exo and endo fashion ring-closure under conditions to afford the title compounds.

Hypervalent iodine-mediated synthesis and late-stage functionalization of heterocycles

“…Another interesting heterocycle, oxazoline 37, was synthesized by Ranjith et al via PIDA-mediated intramolecular oxyacetoxylation of substituted N-allylamides 36 using HF•py as the promoter (Scheme 8). 44 Reaction mechanism initiates with the conversion of PIDA 6 into aryliodinium ion 38 influenced by HF•py, which further interacts with the alkene to form cyclic iodonium ion 39. Next, exo attack by the amide moiety transforms cyclic iodonium ion 39 into alkyl iodane 40.…”

“…In 2016, an intramolecular cyclization of N-(E)-alkenylamides 168 to the corresponding 6-aryl-5-acetoxy-2oxazines 169 induced by PIDA 6 was described by Ranjith et al (Scheme 44). 44 In the proposed mechanism, aryliodinium ion 38 formed from PIDA 6 and HF•py interacts with the alkene 168 and generates cyclic iodonium ion 170 which is attacked by the amide moiety to give alkyl iodane 171. Notably, the presence of aryl group at the end of the alkene stabilizes the incipient carbocation thereby facilitating endo-cyclization of intermediate 171.…”

Synthesis of Oxazoline and Oxazole Derivatives by Hypervalent-Iodine-Mediated Oxidative Cycloaddition Reactions

“…14,51,53,54 Numerous synthetic strategies for the construction of the oxazoline ring have been explored. Particularly important are synthetic approaches using hypervalent iodine reagents, such as (diacetoxyiodo)arenes, [55][56][57][58][59][60][61][62][63][64][65] iodosylarenes, 66 (difluoroiodo)arenes, 67 in situ generated iodine(III) species, [68][69][70][71][72][73] or iodonium ylides. 74,75 This section covers synthetic methodologies for the preparation of various oxazoline derivatives from appropriate substrates using hypervalent iodine species.…”

“…A similar (diacetoxyiodo)benzene-mediated cyclization of N-allylamides 7 in the presence of HF•Py, instead of BF 3 •Et 2 O and acetic acid, gave the respective acetoxymethylcontaining oxazolines 8 in moderate to good yields (Scheme 2). 61 Incidentally, when using substituted N-(E)-allylamides under the same conditions, the reaction resulted in endocyclization due to the carbocation stability to afford the oxazine products instead of oxazolines. (1991), and Doctor of Chemical Sciences (1998) degrees were earned at Tomsk Polytechnic University in the laboratory of Professor Victor D. Filimonov.…”

Copper‐Catalyzed Oxidative C−H Bond Functionalization of N‐Allylbenzamide for Regioselective C−N and C−O Bond Formation

“…The required substrates N-allylbenzamidesw erer eadily prepared from the corresponding benzoyl chloride and allylamine as per our earlier method. [11] At the outset, N-allylbenzamide 1a was chosen ast he model substrate to optimize reaction conditions including the oxidant equivalents, catalyst type, base, solvent, and time as disclosed in Table 1. Accordingly,a preformed solution of N-allylbenzamide 1a (1.0 equiv), TBHP (70 %s olution in water,2 .0 equiv) and CuSO 4 (2.5 mol %) was dissolved in CH 3 CN (2 mL) at room temperature.…”