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13.6.1.1.3.4 Method 4: From an Amidoxime and an Orthoformate

DOI: 10.1055/sos-SD-013-00175

Hemming, K.Science of Synthesis, (200413146.

This method allows access to 3-substituted, 5-unsubstituted 1,2,4-oxadiazoles (9, R2=H) (Scheme 19).[‌115‌] Triethyl orthoformate (35, R2=H) is the most commonly used orthoformate,[‌30‌,‌33‌,‌34‌,‌115‌‌118‌] but trimethyl orthoformate has also been used.[‌118‌] The use of ethyl orthoacetate (35, R2=Me) gives access to disubstituted systems, although a competitive Beckmann-type rearrangement can lead to triazine N-oxides as the major product.[‌116‌] The 3-substituted, 5-unsubstituted 1,2,4-oxadiazoles are usually unstable (although some are unexpectedly stable),[‌34‌] and excess heating can lead to decomposition.[‌1‌‌6‌,‌116‌]

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