Regioselective synthesis of 4- and 5-oxazole-phosphine oxides and -phosphonates from 2H-azirines and acyl chlorides

A simple and efficient regioselective synthesis of 4-oxazole-phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/11" xmlns:xlink="http://www.w3.org/1999/xlink">11</ce:inter-ref> and -phosphonates <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/12" xmlns:xlink="http://www.w3.org/1999/xlink">12</ce:inter-ref> from 2H-azirine-phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/1" xmlns:xlink="http://www.w3.org/1999/xlink">1</ce:inter-ref> and -phosphonates <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/6" xmlns:xlink="http://www.w3.org/1999/xlink">6</ce:inter-ref> is described. The key step for the synthesis of oxazoles <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/11" xmlns:xlink="http://www.w3.org/1999/xlink">11</ce:inter-ref> is a base-mediated ring closure of vinylogous α-aminophosphorus compounds derived from phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/4" xmlns:xlink="http://www.w3.org/1999/xlink">4</ce:inter-ref> and from phosphonates <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/8" xmlns:xlink="http://www.w3.org/1999/xlink">8</ce:inter-ref>. These derivatives <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/4" xmlns:xlink="http://www.w3.org/1999/xlink">4</ce:inter-ref> and <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/8" xmlns:xlink="http://www.w3.org/1999/xlink">8</ce:inter-ref> are obtained by reaction of functionalized azirines <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/1" xmlns:xlink="http://www.w3.org/1999/xlink">1</ce:inter-ref> and <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/6" xmlns:xlink="http://www.w3.org/1999/xlink">6</ce:inter-ref> with acyl chlorides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/2" xmlns:xlink="http://www.w3.org/1999/xlink">2</ce:inter-ref> and subsequent acid-catalyzed ring opening of N-acylaziridine-phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/3" xmlns:xlink="http://www.w3.org/1999/xlink">3</ce:inter-ref> and -phosphonates <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/7" xmlns:xlink="http://www.w3.org/1999/xlink">7</ce:inter-ref>. Regioselective thermal ring cleavage of N-acylaziridine-phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/3" xmlns:xlink="http://www.w3.org/1999/xlink">3</ce:inter-ref> leads α-chloro-β-(N-acylamido)-phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/13" xmlns:xlink="http://www.w3.org/1999/xlink">13</ce:inter-ref> and their treatment with bases gives 5-oxazole-phosphine oxides <ce:inter-ref xlink:href="sid:S0040-4020(04)01111-1/16" xmlns:xlink="http://www.w3.org/1999/xlink">16</ce:inter-ref>. [Copyright &y& Elsevier]