Thieno thiophene-2-carboxylic acid formation

The use of thienyl Grignard reagents, and more recently lithiated thiophenes, has been extensive and can be illustrated by citing formation of oxythiophenes, either by reaction of the former with f-butyl perbenzoate or the latter directly with bis(trimethylsilyl) peroxide or via the boronic acid, the synthesis of thiophene carboxylic acids by reaction of the organometallic with carbon dioxide, the synthesis of ketones, by reaction with a nitrile, or alcohols by reaction with aldehydes, by the reaction of 2-lithiothiophene with A -tosylaziridine, and by syntheses of thieno[3,2- ]thiophene and of dithieno[3,2- 2, 3 - /]thiophene. Some of these are illustrated below. 

The construction of the pyranooxepin system shown in equation (52) proceeds by way of a dibenzox-epinone acetic acid, followed by intramolecular enol ester formation.67 The regioselective cyclization of 4-(2-naphthyloxy)butanoyl chloride proceeds as expected (equation 53) using tin(lV) chloride as the catalyst, but a mixture of products was obtained when the related carboxylic acid was treated with poly-phosphoric acid.68 The preparation of a thieno[fr]suberanone in 40% yield has been achieved by the interaction of tin(IV) chloride with 5-(2-thienyl)valeryl chloride.69 Once again, the expected increase in yield is obtained when cyclization occurs to the 2-position in thiophene. The product shown in equation (54) was isolated in 81 % yield.70 Other intramolecular reactions involving thiophenes have been reported.71... 

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