Grignard entrainment method

Organometallics. Pentachloropyridiae (47) forms Grignard reagent (48) by the entrainment method (eq. 15) (46). Addition of CO2 produces 4-carboxy-2,3,5,6-tetrachloropyridine [19340-26-2]. 

The usefulness of the Grignard reagent of 3-bromothiophene is somewhat limited as it can only be prepared by the entrainment method. The simultaneous formation of Grignard reagents from 3-bromothiophene and a fivefold molar excess of ethyl bromide gave, however, a 55% yield of 3-thiophenecarboxylic acid upon carbona-tion. With acetaldehyde, a 55% yield of methyl 3-thienyl carbinol... 

Although pentacblorophenylmagnesium chloride can be made in tetrahydrofuran without the use of the entrainment method, the Grignard reagent in this solvent does not react with carbon dioxide to give pentachlorobenzoic acid in good yield.10... 

Magnesium, Copper, and Tin. 3-Substituted 4-aryl-2,5-dibromo-thiophens give dimagnesium compounds, when the Grignard reagent is prepared by the entrainment method (simultaneous reaction with... 

By reaction of 3-thienyllithium with magnesium bromide, the Grignard reagent, free from entrainment Grignard reagent, was obtained,- which is useful for the preparation of 3-acetothiophene by reaction with acetic anhydride at —70 0 and for the preparation of 3-t-butoxythiophene through reaction with t-butyl perbenzoate. It is the opinion of the present author that most 3-substituted thiophenes are prepared more conveniently from 3-thienyllithium than from 3-thenyl bromide. The latter method, however, is superior if the introduction of the 3-thenyl group is desired. 

---