A set of acyclic all‐carbon α‐aryl quaternary aldehydes was synthesized by intermolecular palladium‐catalyzed asymmetric allylic alkylation (Pd‐AAA). Hydroxyacrylates were used as unprecedented nucleophilic counterparts instead of widely used ketone substrates. This produced a very rare all‐carbon quaternary aldehyde. Chiral ligand (R,R)‐L3 was found to be optimal in this Pd‐AAA reaction and provided good to excellent yields (75–99 %) and enantioselectivities (75–94 %) with a range of analogs.
A stereoselective synthesis of carbonates derived from 3-hydroxy-2-aryl acrylates was devised that can form the Zor E-stereoisomer in very high Z/E ratios (50:1 and 1:99, respectively). The stereochemical outcome depends on the choice of base, addition of TMEDA and reaction temperature. The Zand E-stereoisomers have different reactivities towards the DAAA reaction, with the E-stereoisomer displaying both greater reactivity and enantiodifferentiation with chiral ligands. The DAAA of E-stereoisomer analogues takes place in excellent yields ranging from 96-99% and enantioselectivities ranging from 42-78% ee.
First Example of the Intermolecular Palladium-Catalyzed Asymmetric Allylic Alkylation of Hydroxyacrylates: Synthesis of All-Carbon -Aryl Quaternary Aldehydes. -A novel intermolecular asymmetric Pd-catalyzed alkylation of 3-hydroxy-2-arylacrylates is developed using a C 2-symmetric diphenylphosphine derivative as catalytic ligand. The process allows the synthesis of -allylated 2-aryl all-carbon quaternary aldehydes in high yields and high enantioselectivities. -(ASAD, S. A.; ULICKI, J.; SHEVYREV, M.; UDDIN, N.; ALBERCH, E.; HOSSAIN*, M. M.; Eur. J. Org. Chem. 2014, 26, 5695-5699, http://dx.
Acrylates 3 were synthesized following a known procedure using a Brønsted acid catalyst, and were converted into the O-allylated products 4 in high yields. The O-allylated products 4 undergo a Claisen rearrangement in refluxing DMF for 6-24 hours, affording compounds 5 with α-aryl quaternary carbon centers in high yields.
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