Palladium-catalyzed reaction of 1,3-diene monoepoxides with .beta.-keto acids. Allylic alkylation and isomerization of 1,3-diene monoepoxides

Pd‐Mediated Reactions of Epoxides

“…), the presence of this latter being required for this rearrangement. [94] On the basis of a proposal by Saegusa et al, [91] we suggest the mechanism depicted in Scheme 19. The reaction would start with the formation of the η 3 -allylpalladium complex 19A.…”

“…[88] In a study of Pd(PPh 3 ) 4 -catalyzed decarboxylative allylic alkylations of 1,3-diene monoepoxides with benzoylacetic acid, Saegusa et al obtained cyclohex-3-enone, rather than the expected alkylation product, from the monoepoxide of cyclohexa-1,3-diene. [91] An unexpected isomerization was also observed by Trost and Angle with the formation of the conjugated cyclohexenone, as shown in Equation (55), from a reaction occurring in the presence of pivalic acid. [92,93] Subsequently, Banwell's team carried out the reaction depicted in Equation (56) with use of the catalytic Pd 2 (dba) 3 · CHCl 3 /dppe system and benzoic acid (1.2 equiv.…”

“…Indeed, 3,4-epoxybut-1-ene and 4,5-epoxyhex-2-ene were benzoylated under these conditions, providing keto allylic alcohols [Equation (64)]. [91] Dienic alcohols can also be obtained from cyclic substrates, as reported in 1988 by Bäckvall and Juntunen, who used a mixture of Pd(dba) 2 and dppe as the catalyst [Equation (65)].…”

“…[88] Saegusa et al observed that these isomerizations can occur at lower reaction temperature and with higher rates in the presence of benzoylacetic acid [Equation (63)]. [91,98] Saegusa's reactions, however, were carried out with larger amounts of catalyst [Equation (63)] and the isomerization pathway involved only a few substrates. Indeed, 3,4-epoxybut-1-ene and 4,5-epoxyhex-2-ene were benzoylated under these conditions, providing keto allylic alcohols [Equation (64)].…”

Ferric chloride-catalyzed decarboxylative alkylation of β-keto acids with benzylic alcohols

“…For a long time the synthetic applications of β-keto acids have been hampered by their instability to heat, acids, and bases [1,2]. Nevertheless, a few appropriate conditions have been reported for β-keto acids to undergo decarboxylative carbon-carbon bond-forming reactions with carbon electrophiles such as aldehydes [1−5], imines [6,7], electron-deficient alkenes [8−10], allylic acetates [11], 1,3-diene monoepoxides [12], and N-benzylic sulfonamides [13]. These biomimetic reactions have demonstrated that β-keto acids are able to serve as attractive surrogates of ketones for α-alkylation because of high reactivity and regioselectivity.…”