Determining substrate selectivity and regiochemistry of nitrilium phosphanylid tungsten complexes in cycloaddition reactions with terminal alkynes

Synthesis of the First 2H-1,2-Azaphosphole Complexes with P,C and P,N Ylide Functional Groups

“…This was established by Xray crystal structure analysis of a 5-(1,5-dimethylpyrrol-2-yl)-substituted 2H-1,2-azaphosphole complex. [9] Furthermore, we found that the regioisomer ratios showed a marked dependence on the C 5 substituent, e.g., 2-furanyl (3:1 ratio), 2-thienyl (5:1 ratio), and 2-(1,5-dimethylpyrrolyl) (8:1 ratio). Therefore, we were interested in examining the regioselectivity of transiently generated nitrilium phosphanylide complexes 2f,g of the general formula RCNP[CH(SiMe 3 ) 2 ]W(CO) 5 [2f: R ϭ Ph 3 PC(H); 2g: R ϭ Ph 3 PN] towards the terminal alkyne derivative 11.…”

“…31 P NMR spectroscopic monitoring of the reaction showed exclusively the formation of the 2H-1,2-azaphosphole complex 8g as the sole phosphorus-containing product, which was isolated in good yields by column chromatography (Scheme 8). As our former studies on the regioselectivity of reaction of transiently generated nitrilium phosphanylide complexes 2a,b [8] and 2cϪe [9] with ethyl acetylenecarboxylate (11) showed, these highly reactive species always yield two regioisomeric 2H-1,2-azaphosphole complexes, with formation of the 4-ethoxycarbonyl-substituted 2H-1,2-azaphosphole complexes being favored. This was established by Xray crystal structure analysis of a 5-(1,5-dimethylpyrrol-2-yl)-substituted 2H-1,2-azaphosphole complex.…”

“…Furthermore, we showed that C-dialkylamino-, C-alkyl-, or C-aryl-substituted nitrilium phosphanylide complexes II reacted with electron-deficient alkynes such as dimethylacetylene dicarboxylate (DMAD) to furnish 2H-1,2-azaphosphole complexes through [3ϩ2]-cycloaddition reactions. [2,8,9] It is noteworthy that only complex 2b, which has Scheme 2. Generation and intramolecular reactions of (nitrilium phosphanylide)tungsten complexes 2a and 3 the dimethylamino group at the carbon atom and a bulky substituent at the phosphorus atom, reacted with DMAD (6) to give both the ∆ 3 -1,3,2-oxazaphospholene complexes 7a,b and the 2H-1,2-azaphosphole complex 8a (Scheme 3).…”

The synthesis of 1,2-azaphospholes, 1,2-azaphosphorines and 1,2-azaphosphepines

“…Also, reaction of complex 56 with ethyl propiolate and different nitriles in pentane gave 1,2-azaphospholes 65 in high yield (Scheme 20). 49,50,52,54…”