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Bromonitrile oxide 2, generated from easily available dibromoformaldoxime 1, reacts with monosubstituted acetylenic derivatives 4 to give 3‐bromo‐5‐substituted isoxazoles 5 in high yield. The experimental conditions necessary to overcome difficulties such as the low reactivity of acetylenic dipolarophiles and the high tendency to dimerization of bromonitrile oxide 2, are discussed; the regioselectivity of this 1,3‐dipolar cycloaddition is also studied. The obtained improvements in the synthesis of some pharmacologically active compounds are reported.

The synthesis of the fluoro analogue (VIII) of thiamphenicol (IX) is reported.

ChemInform Abstract The isoxazolecarboxylic chloride (I) reacts with piperazine (IIa) or 1,4-diazacycloheptane (IIb) to give the amides (III). (IIIa) is coupled with the isothiocyanate (IV), forming the isothiourea (V) which is methylated and then cyclized with formamide (VII) to yield the dimethoxyquinazoline (IX). Tests for antihypertensive activity are conducted in vitro and in vivo in comparison to prazosin.

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