Pd – Allylic Imidate Rearrangement OL03-5-1809
Method from OBC paper.
Ring-closing metathesis with Grubbs I followed by Kharasch cyclisation.
Rearrangement product incorrectly drawn as the S enantiomer in this paper. Correct R enantiomer drawn above.
Pd – Intramolecular aminopalladation JOC05-70-2859
Tosylcarbamate substrates prepared from corresponding allylic alcohol and p-toluenesulfonyl isocyanate.
Pd – Intramolecular allylic substitution JOC10-75-7897
No specific experimental for this reaction – quantity of solvent used not given.
Pd – [3,3]-Sigmatropic rearrangement of allyloxy substituted N-heterocycles OL10-12-260
Pd – O-Allyl Carbamothioate Rearrangement OL08-10-1485
Reaction also performed at RT (67 h, 5 mol% with R1 = n-Pr, R2 = 1-azetinyl, 83% ee) and with 1 mol% cat (47 h, 40 oC, R1 = n-Pr, R2 = 1-azetinyl, 76% ee).
Higher ee with R1 = n-Pr than R1 = Me (for which several examples with <80% ee). Stereospecific N to C aryl migration (#) in some instances resulted in an erosion of ee (slow reaction relative to allyllithium racemisation).
Much lower yield (and reduced e.e.) with COP-Cl. Lower e.e. with (E)-trichloroacetimidates and also competative allylic imidate rearrangement. Reaction temperature of 38 oC with bulkier (slower) carboxylic acids and/or those with lower solubilities. Complete (branched) regioselectivity excepting #. Mechanistic investigations and a model for the basis of enentioselectivity is reported in JACS10-132-15192.
Iterative methodology also extended to the synthesis of all four protected triol enantiomers containing three stereogenic centres. All reactions show essentially complete catalyst control. Methodology further demonstrated by the total synthesis of (+)-solistatin.
Pd – Allylic Aryl Ether Synthesis OL07-9-911
COP-Cl as catalyst gives comparable ee but inferior rate. One example with a branched γ-substituent with R1 = Cy (R2 = 4-OAc, 90% ee, 30% yield, 96 h). R2 = NO2, CN and allyl did not result in product formation.
COP-NHCOCCl3 prepared from COP-OAc and 2,2,2-trichloroacetamide in benzene at 80 oC (azeotropic removal of acetic acid). Use of COP-OAc in the representative reaction resulted in a 59:41 ratio of phenyl ether (91% ee) to allylic imidate rearrangement product. With COP-NHCOCCl3 the corresponding ratio is 92:8.
Pd – Enantioselective synthesis of 2-vinyl oxygen heterocycles JOC12-77-1961
Use of COP-Cl instead of COP-OAc resulted in competitive allylic imidate rearrangement. A very low ee resulted from a corresponding Z substrate. Acetates rather than trichloroacetimidates may be used for the synthesis of 2-vinylchromanes resulting in similar enantioselectivities although with a higher catalyst loading (2 mol%) and with 1 eq. of KF as additive.