Benzo phosphole synthesis

The alkyne-phosphine condensation can be performed in intramolecular fashion, allowing the synthesis of the benzo[(>]phosphole (phosphindole) ring system, as seen in Scheme 60. The phos-phindoles were obtained in 90-96% yield <93TL3103>. 

The method consists of the one-step synthesis of (Z)-l,2-(bis-benzo-dithienyl)ethenes 10 using double Suzuki coupling between stereochemi-caUy defined diboronic acid esters 11 and 2-iodo-benzodithiophene 12. The (Z)-alkenes thus obtained can be easily and efficiently photochemicaUy cyclized to the corresponding substituted tetrathia[7]helicenes. This methodology can also be applied to the synthesis of stilbenoid derivatives with two different heterocyclic systems such as the phosphole 13 (Figure 3) (2014CEJ12373). 

MatanoY, MiyajimaT, FukushimaT, Kaji H, Kimura Y, Imahori H (2008) Comparative study of the synthesis, structures, and optical and electrochemical properties of bithiophene-fused benzo[c]phospholes. Chem Eur J 14 8102-8115... 

Silver-mediated annulations of the allg nes (705) by arylphosphinates (706) via C-H/P-H functionalisation has been described as a step-economical route to synthesis of substituted benzo[Z)]phospholes (707) (Scheme 195). ... 

Phospholes are known to exhibit characteristic optical and electrochemical properties derived from the phosphorus-bridged 1,3-dienic jt system [34]. Particular interest has recently been paid to their Jt-conjugated derivatives, such as nonfused phospholes, dibenzo[f ,d] phospholes, benzo[f ] phospholes, benzo[c] phospholes, and related compounds [35]. There are several methods to synthesize phospholes [36]. The classical method for the synthesis of phospholes is the reaction between the nucleophilic substitution of a P-X bond with a stoichiometric amount of an organometallic species such as organolithium or organomagnesium reagents (Scheme 4.21) [37]. 

Scheme 9.38 Synthesis of Benzo[6]phosphole Oxides through Silver-Mediated C-H Activation.

Scheme 9.39 Possible Mechanism of Silver-Mediated Synthesis of Benzo[b]phosphole Oxides.

Scheme 10.10 Synthesis of benzo[b]phospholes through one-pot multicomponent coupling.

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