Stereoselective Intermolecular [4+2] Process of N,O‐acetals with Terminal Alkynes for Construction of Functional cis‐Pyrido and Pyrrolo[1,2‐c][1,3]oxazin‐1‐ones

Abstract

A diastereoselective approach to access cis‐pyrido and pyrrolo[1,2‐c][1,3]oxazin‐1‐ones has been developed through a one‐pot BF3.Et2O‐catalyzed [4+2] process starting with N,O‐acetals and terminal alkynes. In addition, the utility of this transformation is demonstrated by the scalable synthesis of (+)‐Febrifugine in 7 steps from the N,O‐acetal (15% overall yield).

A Ag2CO3/TFA-catalyzed intramolecular annulation approach to imidazo[1,2-c][1,3]oxazin-5-one derivatives

“…In order to prepare a library of new imidazo[1,2- c ][1,3]oxazin-5-one heterocycles, N -Boc-4-bromo-5-methyl-2-phenylethynylimidazole 1a was studied as a model substrate and subjected to some annulation process conditions which have been already described in the literature. 25,37,46,49,50,57–64 Compound 1a , which is a suitable substrate for undergoing intramolecular annulation, was prepared following our recent procedure involving the regioselective Sonogashira cross coupling reaction of N -Boc-2,5-dibromo-4-methylimidazole. 48 Initially, the zinc catalyst (ZnCl 2 ) was used in dichloromethane at 40 °C but it was found to be totally inert since the starting material was completely recovered after 48 h (Table 1, entry 1).…”

Synthesis of Amide Enol Carbamates and Carbonates through Cu(OTf)2-Catalyzed Reactions of Ynamides with t-Butyl Carbamates/Carbonates

“…On the basis of our obtained experimental results and the precedent ynamide chemistry, , a possible mechanism for this Cu­(OTf) 2 -catalyzed transformation is illustrated in Figure . First, the triple bond in ynamides 4 was activated by copper­(II) triflate.…”

“…Enol carbamates have been recognized as integral structural motifs of pharmaceuticals and agrochemicals and have also served as versatile synthons in organic transformations . Very recently, we found that the carbonyl oxygen atom of the Boc group could attack ynamide-derived intermediates upon the cleavage of the t -butyl–O bond under Lewis acid conditions . The driving force of this novel transformation intrigued us to investigate the potential of such nucleophilic addition directly onto the triple bond of ynamides.…”

A One-Pot Approach to 2-Substituted-2-(Dimethoxyphosphoryl)-Pyrrolidines from Substituted tert-Butyl 4-Oxobutylcarbamates and Trimethyl Phosphite

“…δ-Amino α-diazo β-ketophosphonate has also been converted to 3-oxo pyrrolidine phosphonate via an intramolecular metal carbenoid N–H insertion (Figure , e) . On the basis of our continuous efforts in establishment of azaheterocyclic building blocks, we envisioned that the addition-phosphates of the carbonyl containing amides could occur. Herein we present this effective approach to 2-substituted-2-(dimethoxyphosphoryl)-pyrrolidines through the intramolecular condensation and phosphatization process (Figure , f).…”