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Abnormal aza-Wittig reaction on the solid-phase: chemoselectivity studies towards the parallel synthesis of 3-aryl-2,4-dioxo-1,3,5-triazino[1,2-a]benzimidazoles

✍ Scribed by Cornelia E Hoesl; Adel Nefzi; Richard A Houghten

Publisher
Elsevier Science
Year
2003
Tongue
French
Weight
338 KB
Volume
44
Category
Article
ISSN
0040-4039

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✦ Synopsis

An abnormal aza-Wittig reaction was observed when resin-bound iminophosporanes were treated with aryl isocyanates on the solid-phase. The mechanism of the reaction may involve the loss of triphenylphosphinimide instead of triphenylphosphinoxide, resulting in the formation of isocyanates instead of carbodiimides as intermediates. The selectivity of the abnormal aza-Wittig reaction versus the normal aza-Wittig reaction was shown to be strongly dependent on the reaction temperature and the nature of the aryl isocyanate employed. Optimization studies revealed that employing electron poor aryl isocyanates at high temperature leads to 95% of abnormal aza-Wittig product. The reaction was used for the parallel solid-phase synthesis of 3-aryl-2,4-dioxo-1,3,5-triazino[1,2-a]benzimidazoles.

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## Abstract The reaction of (E)‐3‐aryl‐2‐propenoic acid derivatives with (N‐isocyanimino) triphenylphosphorane proceeds smoothly at room temperature to afford the corresponding 2‐[(E)‐2‐aryl‐1‐ethenyl]‐1,3,4‐oxadiazole via an intramolecular aza‐Wittig reaction in good yields under neutral condition