Reactions of Pivaloin Derivatives with Lithium Tetramethylpiperidide

Article abstract of DOI:10.1021/jo01300a031

The reaction of lithium tetramethylpiperidide (LiTMP) with a series of derivatives of pivaloin has led to a variety of unusual transformations.The reaction of LiTMP with the triflate derivative of pivaloin (7) gave the reduced ketone 2,2,5,5-tetramethyl-3-hexanone (9), which is suggested to arise via electron transfer from LiTMP.A labeling study confirmed that α-proton abstraction from 7, giving an enolate anion, did not occur.The mesylate derivative of pivaloin (16) on treatment with LiTMP gave both isomers of 2,2,6,6-tetramethylhept-4-en-3-one (17 and 18) in which an additional carbon was incorporated into the carbon skeleton.A mechamism involving deprotonation of the methyl group of the mesyloxy function followed by intramolecular cyclization into the carbonyl function and subsequent reaction is suggested to account for this transformation.The acetate derivative of pivaloin (26) gave a cyclized product derived from proton abstraction from the methyl group of the acetoxy function, while the tosylate derivative of pivaloin (30) gave a product derived from proton abstraction from the ortho position of the aromatic ring.The α-bromo ketone 4-bromo-2,2,5,5-tetramethyl-3-hexanone (38) was reduced to ketone 9 with LiTMP.Reaction of triflate 7 and the triflate derivative of 3-hydroxycamphor (43) with potassium tert-butoxide gave the diketones 2,2,5,5-tetramethyl-3,4-hexanedione (8) and camphorquinone (44), respectively, by β elimination of trifluoromethanesulfinic acid.