Controlled Synthesis of 1,3,5-Oxadiazin-2-ones and Oxazolones through Regioselective Iodocyclization of Ynamides

Abstract

Two efficient processes based on the iodocyclization of ynamides have been developed: (i) N-alkynyl tert-butyloxycarbamates were found to undergo a rare 6-exo-dig ring closure reaction affording 1,3,5-oxadiazin-2-ones by using acetonitrile as solvent; (ii) In the absence of acetonitrile, N-alkynyl tert-butyloxycarbamates could undergo 5-endo-dig cyclization providing oxazolones.

Crystal structure of (Z)-2-((2-bromo-1-phenylvinyl)oxy)benzonitrile, C15H10BrNO

“…In recent years, bromoalkynes have emerged as versatile and useful building blocks in a variety of synthetic transformations, which can be generally designed as a dual functionalized molecules and di erent reaction intermediates to synthesize all kinds of new compounds with other organic molecules [1][2][3][4]. Bond lengths and bond angles within the molecular system are in agreement with the values reported [5,6].…”

Generation of Oxazolidine‐2,4‐diones Bearing Sulfur‐Substituted Quaternary Carbon Atoms by Oxothiolation/Cyclization of Ynamides

“…Cyclization of ynamides containing leaving groups such as Et and i Pr took place with poor yields (Table , entries 1 and 2). As we reported before, N ‐alkynyl tert ‐butyloxycarbamates are structures of great potential for the synthesis of cyclic carbamates, and N ‐alkynyl tert ‐butyloxycarbamate 6 ac reacted well to offer the desired product in good yield (Table , entry 3). Furthermore, N ‐carbobenzyloxy‐protected ynamide ( 6 ad ) furnished the corresponding product in 51 % yield, which is relatively lower than that obtained with 6 ac (Table , entry 4).…”

Metal‐Free Synthesis of Oxazolidine‐2,4‐diones and 3,3‐Disubstituted Oxindoles via ICl‐Induced Cyclization

“…To our delight, (diacetoxyiodo)benzene in combination with potassium iodide[14a] or trimethylsilyl iodide[14b] was also effective for promoting the desired iodolactonization of N ‐Boc acrylamide 1a , which normally are ineffective in similar transformations (Table , entries 1–2). The O ‐cyclization product 2a arose from nucleophilic attack of the carbamate carbonyl group on the double bond, and the structure of this compound was established by two‐dimensional (2D) NMR experiments and HRMS experiments. Molecular iodine and N ‐iodosuccinimide (NIS), which are commonly used in iodocyclization reactions, could also be used for iodolactonization of 1a , but the yields were generally lower than PhI(OAc) 2 ‐induced reactions (entries 3–4).…”