Web Release Date: March 3,
Radical Scission of Symmetrical 1,4-Dicarbonyl Compounds: C-C Bond Cleavage with Titanium(IV) Enolate Formation and Related Reactions
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307
Received August 9, 2001
Abstract:
Reaction of Ti(NRAr1)3 (1, R = C(CH3)3, Ar1 = 3,5-C6H3Me2) with 0.5 equiv of symmetrical
1,4-diketones (ArCOCH2)2 (Ar = p-Tol or p-MeOC6H4) in hydrocarbon solvents at 
25 
C
resulted in carbon-carbon bond cleavage with clean formation of titanium-bound enolates,
1-OC(CH2)Ar. Treatment of Ti(NRAr1)3 with esters or amides of succinic acid, under the
same mild conditions, smoothly produced titanium(IV) compounds containing the corresponding amide or ester enolate moiety. The amide enolate condenses with benzaldehyde
in an aldolic fashion. Differences in the observed reactivity of amido-enolate vs ketone-derived
enolate toward aldol condensation were interpreted with the help of computational methods.
Upon reaction with Ti(NRAr1)3, para-substituted acetophenones yielded equal amounts of
enolate and alkoxide products. Under similar experimental conditions, acetophenone itself
produced quantitatively a species whose proposed structure incorporates characteristics
reminiscent of a Gomberg dimer. This intermediate decomposes cleanly to the expected
enolate and alkoxide mixture upon heating. Ti(NRAr1)3 reductively complexes substrates
such as N-methyl phthalimide. Treatment of Ti(NRAr1)3 with 0.5 equiv of o-bromophenyl
allyl ether resulted in bromine atom abstraction followed by cyclization of the intermediate
aryl radical to generate a titanium-bound 3-methylenedihydrobenzofuran product.
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