PCl3 mediated cyclization: Synthesis, at room temperature, of N-alkenyl derivatives of 1,4-phthalazinedione

✍ Scribed by Graziano Baccolini; Carla Boga; Umberto Negri

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 198 KB
• Volume: 10
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/(sici)1098-1071(1999)10:4<291::aid-hc5>3.0.co;2-#

✦ Synopsis

The use of a PCl 3 /hydrazone/dicarboxylic acid combination can be applied in an efficient one-pot procedure for the synthesis at room temperature of the title ring compounds that are also a new family of stable enamines. The phthalazinediones 7 were obtained in good yields by reaction of PCl 3 with phthalic acid and hydrazones 1a,b,c containing hydrogen atoms only in one ␣ position. Two structurally isomeric phthalazinediones (7 and 8) were obtained with hydrazones 1d,e,f,g containing hydrogen atoms in the two different ␣ positions. When we used a methyl ketone hydrazone 1c,d,e,f,i, it was possible also to isolate the isomer containing an N-alkenyl group with two terminal hydrogen atoms. Where E,Z isomers are possible, the exclusive formation of the E isomer was always observed. As a rule, changing the order of addition of reagents gave almost identical results; however, in the case of phthalic acid, it is better to use the procedure in which PCl 3 is added last to prevent the formation of the corresponding anhydride.