Mechanistic Insights into the Palladium^II-Catalyzed Hydroxyalkoxylation of 2-Allylphenols

Abstract

The Pd(OCOCF3)2/[(HOCH2CH2NHCOCH2)2NCH2]2-catalyzed oxidation of o-allylphenol with H2O2 in water/methanol affords a syn and anti mixture of 2-(1,2-dihydroxypropyl)phenol and 2-(2-hydroxy-1-methoxypropyl)phenol. Mechanistic experiments and ESI-MS studies support a pathway wherein isomerization of the C=C bond followed by its epoxidation and oxirane opening led to the products. Recycling of the catalytic system led to gradual lost of activity.

Solvent‐Enhanced Diastereo‐ and Regioselectivity in the PdII‐Catalyzed Synthesis of Six‐ and Eight‐Membered Heterocycles via cis‐Aminopalladation

“…With regards the underlying mechanism, if the reactions proceeded via a p-allyl-palladium intermediate, seven-membered heterocycles would also have been formed, in accord with the results of Beccalli et al [4] In view of the marked difference between the electron density of the tosyl-protected aniline-type nitrogen and the protected cyclohexylaminetype nitrogen, we suggest that, after a Pd-mediated double bond migration, [9,10] the ring-closure towards 9-13 and 17 takes place via cis-aminopalladation, [1k] due to the stronger coordination of the protected cyclohexylamine-type nitrogen to the palladium moiety. (Scheme 4).…”

“…The combined organic phase was dried over anhydrous Na 2 SO 4 and evaporated to dryness under reduced pressure. The residue was purified by column chromatography (n-hexane/ethyl acetate 4:1), which provided pure compounds 9-15, 17, 18, 23 and 24. (2R * ,4aR -vinyl-2,3,4a,5,6,7,8,8a-octahydro-1H-quinazolin-4-one (9) 4, 24.7, 24.9, 30.9, 39.9, 45.3, 53.0, 69.8, 117.5, 119.9, 126.8, 130.1, 132.4, 136.4, 136.9, 144.0, 166.7 ppm;IR (KBr): ñ = 3079, 2960, 2942, 2865, 1935, 1655, 1445, 1343, 1246, 1168, 1090 14,H 7.00,N 7.48;found: C 64.02,H 7.12,2,6a,7,8,9,10, 4, 23.9, 24.9, 28.6, 28.7, 41.9, 44.4, 49.4, 58.2, 117.1, 118.1, 126.9, 127.0, 130.3, 134.1, 138.8, 143.4, 171.8 ppm;IR (KBr): ñ = 3085, 3067, 2924, 2864, 1935, 1834, 1654, 1445, 1396, 1336, 1221, 1154, 1090 14,H 7.00,N 7.48;found: C 64.01,H 6.82,3,6a,7,8,9,10, -4,6-dione (24): Pr...…”

Pd‐Mediated Reactions of Epoxides

“…[34] A similar epoxide opening was observed with 2-[2-(benzyloxy)phenyl]-3-methyloxirane [Equation (14)]. [33] …”

“…The Pd II -catalyzed oxidation of (E)-2-(prop-1-enyl)phenol with H 2 O 2 in aqueous methanol affords a mixture of 2-(1,2-dihydroxypropyl)phenol and 2-(2-hydroxy-1-methoxypropyl)phenol [Equation (13)]. [32] We demonstrated that this reaction involves the formation of an epoxide as the intermediate; [33] this was favored by the phenolic OH. [34] A similar epoxide opening was observed with 2-[2-(benzyloxy)phenyl]-3-methyloxirane [Equation (14)].…”

“…Unlike Pd 0 catalysts, which convert 2,3-epoxycyclohexanones into cyclohexane-1,3-diones [Equation (33)], Pd(OAc) 2 and PdCl 2 lead mainly to cyclohexene-1,2-diones [Equation (35)]. [61] This isomerization, discovered by Larhed and co-workers, was used for the one-pot synthesis of 3-arylcyclohexane-1,2-diones from 2,3-epoxycyclohexanone and aryl bromides.…”