An easy route to 2‐substituted‐2,3‐dihydro‐5(7)H‐oxazolo[3,2‐a]pyrimidin‐5‐ones and 7‐ones starting from the corresponding 2‐amino‐2‐oxazolines

Abstract

An easy Route to 2-Substituted-2,3-dihydro-5(7)H-oxazolo [3,2-a]pyrimidin-5-ones and 7-ones Starting from the Corresponding 2-Amino-2-oxazolines I. Forfar [a], J. Guillon [a], S. Massip [a], J.-M. Léger [a], J.-P. Fayet [b] and C. Jarry [a] [a] EA 2962 -The isomeric 2-substituted-7(5)-methyl-2,3-dihydro-5(7)H-oxazolo[3,2-a]pyrimidin-5-ones 3a-b and 7-ones 2a-b,7a were synthesized by cyclocondensation from the 5-substituted-2-amino-2-oxazolines 1a-b with biselectrophiles. In boiling ethanol, the reaction of 1a-b with acetylenic esters led to a mixture of 2a-b,7a with a small amount of (E)-2-N-(2-ethoxycarbonylethylene)-5-substituted-2-iminooxazolines 5a-b. The ring annulation between 1a-b and diketene gave the 2-substituted-7-hydroxy-7-methyl-2,3,6,7tetrahydro-5H-oxazolo[3,2-a]pyrimidin-5-ones 4a-b which can be easily dehydrated to provide the 2-substituted-7-methyl-2,3-dihydro-5H-oxazolo[3,2-a]pyrimidin-5-ones 3a-b.

Simple and Expedient Access to Novel Fluorinated Thiazolo- and Oxazolo[3,2-a]pyrimidin-7-one Derivatives and Their Functionalization via Palladium-Catalyzed Reactions

“…Continuing our interest in the development of efficient methods for the synthesis of new fluorinated heterocyclic compounds with possible biological properties [41][42][43][44][45][46][47], we Classically, Thiazolo and oxazolo[3,2-a]pyrimidin-7-one derivatives have been synthesized by reactions of the corresponding 2-aminoazoles with a symmetric alkyne such as dialkyl acetylenedicarboxylates [28][29][30][31][32][33][34][35][36] (Figure 2a), or an asymmetric alkyne such as ethyl propiolate derivatives [37][38][39][40] (Figure 2b). However, despite their relevance, these procedures have several drawbacks such as a lack of generality, poor regioselectivity, the use of expensive reagents or less available reagents, as well as unsatisfactory yields.…”