2-Iodo-5-methylthiophene

In the direct synthesis of aryl terminal alkynes via Pd-catalyzed cross-coupling of aryl halides with ethynylmetals, formation of diarylethynes is one of the potential side reactions. Indeed, the Kumada coupling of 2-iodo-5-methylthiophene (29) with ethynylmagnesium chloride gave the desired 2-ethynyl-5-methylthiophene (30) in only 35% yield, along with 24% of bis(5-methyl-2-thienyl)ethyne (31) [29], The high propensity for H-Mg exchange reaction to occur was blamed for the diarylethyne formation. 

Indeed, the Kumada coupling of 2-iodo-5-methylthiophene (43) with ethynylmagnesium... 

The first example of alkylthiophene bromination was also demonstrated at that time. Methylthiophene which was obtained from coal tar as a mixture with toluene was reacted with bromine, and dibromo(methyl)thiophene separated from toluene. Its further bromination led to the synthesis of fully substituted tribromo(methyl) thiophene. 2-Iodo-5-methylthiophene was obtained by the same iodination procedure as iodothiophene. Deiodination with sodium allowed for the isolation of pure methylthiophene [80]. 

A New Improved Synthesis of Tricycle Thienobenzazepines Apphcation of chemistry recently developed by Knochel" combined with the well-described halogen dance (HD) reaction, allowed preparation of our key intermediate A in only three synthetic transformations (Scheme 6.4). In this respect, treatment of 2-bromo-5-methylthiophene with hthium diisopropylamide followed by dimethylformamide afforded aldehyde 11 in good yield, lodo-magnesium exchange with conunercial 4-iodo-3-nitro anisole followed by reaction with 11 afforded the thiophene catbinol 12. Dehydroxylation of 12 provided our key intermediate A which presented the requisite functionality to examine our approach to the construction of the seven-member ring system. 

The photochemical substitution of some iodo substituted pyrroles 1446 in the presence of an aromatic compound (benzene, w-xylene, thiophene, 2-chlorothiophene, 2-methylthiophene) varies with the structure of the pyrrole and reaction conditions and gives the corresponding aryl derivatives 1447 and/or dehalogenated product 1448 (Equation 299) <1997J(P1)2369>. 

Chloromercuri)-3-methylthiophene is converted by aqueous iodine-potassium iodide solution into 2-iodo-3-methylthiophene in 92% yield,751 and the readily accessible 2,5-bis-(chloromercuri)-3-methylthiophene752 into 2,5-diiodo-3-methylthiophene in 70% yield.751 The mono- and bis-(chloromercuri) derivatives of 2,5-dimethylfuran give analogously 3-iodo-and 3,4-diiodo-2,5-dimethyIfuran, respectively.753... 

Thallation of thiophens in the 2-position with thallium(m) trifluoro-acetate in trifluoroacetic acid is complete within a few minutes at room temperature. The thallium derivative reacts in situ with aqueous potassium iodide solution to give a convenient and high-yield synthesis of iodo-thiophens. A mixture of thallium(m) acetate has been shown to be a mild and efficient reagent for electrophilic aromatic bromination. Thiophen yields 2-bromothiophen in 82% yield and very little dibromothiophen. 3-Methylthiophen appears to be selectively brominated in the 2-position and 2-methylthiophen in the 5-position in 70—75% yield. The direct thiocyanation of thiophen and some alkylthiophens with thiocyanogen under various conditions using a variety of Friedel-Crafts catalysts has... 

The metallation of thiophen and 2- and 3-methylthiophen with butylcaesium and butylpotassium has been studied. Thienylcopper reagents have been used for the synthesis of iodo-thiophens. Thienyltin(iv) compounds have been prepared. The chemistry of thienyl-lead(iv)tricarboxylate has been investigated. The cleavage of the thiophen-silicon bond in tris(trichloro-2-thienyl)-methylsilane with butyl-lithium to give thienyl-lithium derivatives has been achieved. Considerable work on the synthesis and reactions of compounds containing thiophen-phosphorus bonds has appeared/ " and the reactions with a/S-unsaturated acid derivatives have been extensively studied. ... 

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