Facile control of regioselectivity in the reaction of tin enolates with α-halogeno carbonyls by additives

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Abstract
Tin enolates 1 reacted with α-halogeno ketones 2 and esters 10 to give a variety of 1,4-diketones 3 and γ-keto esters 11, respectively, in the presence of appropriate additives such as hexamethylphosphoric triamide (HMPT), tributylphosphine oxide and tetrabutylammonium bromide, while complexation of these additives with tributyltin bromide allowed catalytic production of β-keto oxiranes 4 instead of 3. The reaction mechanism for the preparation of 1,4-diketone 3 is discussed.