Stille coupling pyrroles

Bailey described the first application of the Stille coupling to pyrroles, and one of the earliest examples of any such reaction involving heterocycles [66]. Lithiation of IV-methylpyrrole and quenching with trimethylstannyl chloride gives 2-(trimethylstannyl)pyrrole (76), and palladium-catalyzed coupling with iodobenzene affords l-methyl-2-phenylpyrrole (46) in good yield. 

Stille couplings on W-protected derivatives of 85 proceed well, as shown below for the synthesis of pyrroles 86 [70]. 

Dubac has employed a Stille coupling reaction to synthesize the pyrroles 88 and 89 from stannylpyrrole aldehyde 87 [71]. The latter tin compound was prepared as shown, and related stannylpyrroles were synthesized similarly [72] or using Muchowski s 6-dimethylamino-l-azafulvene dimer lithiation methodology [73]. 

Stille couplings between stannylpyrrole 92 and siloles 93 and 94 have afforded the silole-pyrrole 95 [75]. These workers also prepared dimers and trimers of 95. 

The Pd-catalyzed cross coupling reaction of 3-stannylated pyrroles is also known. Muchowski has thus prepared and utilized 96 to effect Stille couplings leading to 97 [59]. 

Pyrrole 98 has been employed in Stille couplings with dibromobenzoquinone 99 [76]. The product 100 can be subjected to a second Stille coupling to afford unsymmetrical diheteroarylquinones. Similar couplings between 98 and 2,3-dibromo- 1,4-naphthoquinone were also described. 

Halogenated pyrroles can serve as the aryl halide in Stille couplings with organotin reagents. Scott has used this idea to prepare a series of 3-vinylpyrroles, which are important building blocks for the synthesis of vinyl-porphyrins, bile pigments, and indoles [77]. Although 3-chloro-and 3-bromopyrroles fail completely or fared poorly in this chemistry, 3-iodopyrroles 101 work extremely well to yield 3-vinylpyrroles 102. 

These workers have also used 3-iodopyrrole 103 to prepare the corresponding tin derivative 104 for Stille couplings to furnish 3-arylpyrroles 105 [78], These pyrrole derivatives are important for the synthesis of (i-aryl-substituted porphyrins for studies of heme catabolism. Also synthesized in this study were compounds 106 and 107 [78]. 

A low band-gap (Eg 1.6 eV) conjugated thiophene copolymer 468 with pyrrole and BT units was synthesized by Stille coupling [568]. They showed emission in the NIR region (AEL 800 nm) with turn-on voltage below 4 V but with very low efficiency (Chart 2.113). 

PPys synthesized by both oxidative routes are also subject to coupling defects, which drastically reduce sought after properties. To circumvent this problem, transition metal-mediated polymerizations have been explored. Once again, the synthetic inflexibility of the pyrrole moiety has proven to be a formidable obstacle in obtaining such materials. The Stille coupling scheme [12], shown in Scheme 60, has been used to prepare a BOC-substitued PPy 63 with the protecting group subsequently removed by thermolytic treatment to yield unsubstitut-... 

A Stille coupling between stannylpyrrole 136 and 3-bromoindole 137 gave the expected 138 albeit in low yield [63]. Pyrrole 136 was prepared from 80 in the usual manner (1. n-BuLi 2. Bu,SnCl 65%). 

Similarly, Hibino et al. achieved excellent yields of 2-vinylpyrroles 168 via Stille coupling of pyrroles 167 and tributylvinylstannane [100]. 

Dipyrrolylquinoxalines with extended ehromophores are efficient fluorimetric sensors for pyrophosphate. The Stille coupling of 5,8-dibromo-2,3-di(pyrrol-2-yl) quinoxaline with aryItributylstannane produced 5,8-diaryl substituted quinoxalines 205 as possible sensors [100]. 

Pyrrole ring containing polymers have been synthesized via Stille coupling of 2,5-bis(5-(trimethylstannyl)-2-thienyl)-Af-dodecylpyrrole and... 

Chu et al reported a new alternating copolymer of dithienosilole and thieno-pyrrole-4,6-dione (P3), which was synthesized by Stille coupling of a ditin compound and dibromo compound in refluxing toluene/dimethylformamide (10 1) with Pd(PPh3)4 as the catalyst. The purified pofymer has a of 28 kDa and a PDI of 1.6, as determined by GPC using chlorobenzene (CB) as the eluent. P3... 

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