Claisen condensation with malononitrile

If two equivalents of the 2-halo-carbonyl compound (or 2-halo-nitrile) are utilised to react with an enolate/carbon disulfide adduct, double S-alkylation and then double ring closure produce thieno[2,3-h]thiophenes [129] Scheme 82 shows how this works. Taking this idea further, if a malonate is used as the 1,3-dicarbonyl component, 3,4-dihydroxythieno[2,3-h]thiophenes are the final result (Scheme 83) [130], the ring closure steps then having the character of Claisen condensations. If malononitrile is used instead of a 1,3-dicarbonyl compound, the product is a 3,4-diaminothieno[2,3-6]thiophene - product 60 in Scheme 84 is the result of using chloroacetonitrile in the alkylation step [131]. 

A. tert-Butylmalononitrile. In a dry 2-1. three-necked flask equipped with a thermometer, mechanical stirrer, and a Claisen adapter fitted with a dropping funnel and condenser protected with a drying tube is placed 200 ml. of nitromethane (Note 1). The flask is cooled to 0° in an ice-salt bath (Note 2), and anhydrous powdered aluminum chloride (90.0 g., 0.68 mole) is added with slow stirring through a powder funnel that temporarily replaces the thermometer. The temperature may rise to ca. 50° but quickly drops to 0°. Malononitrile (45.0 g., 0.68 mole) (Note 3) in 50 ml. of nitromethane is added through the dropping funnel at a rate such that the temperature is kept below 10° (approximately one hour), followed by slow dropwise addition of tert-butyl chloride (Note 4) (150 g., 1.62 moles) in 50 ml. of nitromethane at a rate such that the temperature is maintained... 

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