2- Lithio-l-methylpyrrole

A Heck coupling of 2-lithio-l-methylpyrrole and bromohydrin 153 affords 154 [112]. 

Carbonsulfur bonds can be formed by the reaction of elemental sulfur with a lithio derivative, as illustrated by the preparation of thiophene-2-thiol 446. If dialkyl or diaryl disulfides are used as reagents to introduce sulfur, then alkyl or aryl sulfides are formed sulfinic acids are available by reaction of lithium derivatives with sulfur dioxide. In the pyrrole series, a 2-thiol and the corresponding selenol can be prepared via reaction of 2-lithio-l-methylpyrrole with sulfur or selenium, then trapping with Me3SiCl leading to the 2-Me3SiX-substituted derivatives <1997T13079>. 

Treatment of 2-lithiothiophene or 2-lithio-l-methylpyrrole (49) with R3B (R = alkyl, phenyl), then iodine or Af-chlorosuccinimide (NCS), gives 2-substituted derivatives of thiophene or l-methylpyrrole (50), respectively (Scheme 19). The reaction can be rationalized by considering the initial electrophilic attack on the heteroaryl ring with spontaneous 1,2-migration of the R group, followed by dehaloboration (79BCJ1865, 79TL2313). 

The methyl ester of l-methylpyrrole-2-carboxylic acid can be prepared in a similar way from 2-lithio-l-methylpyrrole (prepared as described in Exp. 8) and CICOOCH3. The boiling point of the ester is ca. 50 °C/0.5 mm, n 2 1.5132, the yield is 65 %. 

A suspension of 2-lithio-l-methylpyrrole in ca. 80 ml of hexane is prepared from... 

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