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Knorr, Rudolf; Menke, Thomas; Freudenreich, Johannes; Pires, Claudio (2014): Carbenoid-mediated nucleophilic "hydrolysis" of 2-(dichloromethylidene)-1, 1, 3, 3-tetramethylindane with DMSO participation, affording access to one-sidedly overcrowded ketone and bromoalkene descendants. In: Beilstein Journal of Organic Chemistry, Vol. 10: pp. 307-315


2-(Dichloromethylidene)-1, 1, 3, 3-tetramethylindane was "hydrolyzed" by solid KOH in DMSO as the solvent at >= 100 degrees C through an initial chlorine particle transfer to give a Cl, K-carbenoid. This short-lived intermediate disclosed its occurrence through a reversible proton transfer which competed with an oxygen transfer from DMSO that created dimethyl sulfide. The presumably resultant transitory ketene incorporated KOH to afford the potassium salt of 1, 1, 3, 3-tetramethylindan-2-carboxylic acid (the product of a formal hydrolysis). The lithium salt of this key acid is able to acylate aryllithium compounds, furnishing one-sidedly overcrowded ketones along with the corresponding tertiary alcohols. The latter side-products (ca. 10%) were formed against a substantially increasing repulsive resistance, as testified through the diminished rotational mobility of their aryl groups. As a less troublesome further side-product, the dianion of the above key acid was recognized through carboxylation which afforded 1, 1, 3, 3-tetramethyl-indan-2, 2-dicarboxylic acid. Brominative deoxygenation of the ketones furnished two one-sidedly overcrowded bromoalkenes. Some presently relevant properties of the above Cl, K-carbenoid are provided in Supporting Information File 1.