Hazumi Nomura

Stabilized bismuthonium ylides bearing a highly cross-conjugated ylidic carbon atom: synthesis, structures, and reactions

Abstract The reaction of iminotriaryl-λ 5 -bismuthanes ( 2 ; Ar 3 BiNR; R=COR″ or SO 2 R″) with dialkyl acetylenedicarboxylates ( 3 ; R′O 2 CCCCO 2 R′) has been found to afford highly stabilized bismuthonium ylides ( 4 ; Ar 3 BiC(CO 2 R′)C(CO 2 R′)NR) in 50–92% yield. The X-ray crystallographic analyses of two of these ylides demonstrated that their bismuth center possesses a distorted tetrahedral geometry with the highly cross-conjugated ylidic carbon atom. The observed BiC ylide bond lengths of 2.178(7)–2.199(7) A are close to ordinary BiC Ar bond lengths, suggesting an appreciable single bond character of the BiC ylide bond. The action of two equivalents of acetic acid, hydrogen chloride, or 4-nitrophenol on 4 cleaved the BiC ylide bond to give the corresponding triarylbismuth(V) compounds of the type Ar 3 BiX 2 and olefins ( 5 ; R′O 2 CCHC(CO 2 R′)NHR). 4-Nitrobenzenethiol was oxidized by 0.5 equivalents of 4 to give bis(4-nitrophenyl) disulfide with a good recovery of triarylbismuthane 6 and olefin 5 . On thermolysis at 200°C, or when decomposed in the presence of a copper catalyst at room temperature, the ylides 4 bearing an N -aroyl group gave 2,4,5-trisubstituted oxazoles 7 and triarylbismuthanes 6 in moderate to excellent yields.