On the regiochemistry of nucleophilic attack on 2-halo pi-allyl complexes. 4. The effect of silver acetate and nucleophile concentrations in competitive nucleophilic attack with malonate and phenoxide nucleophiles.

2,3-Dibromo-1-propene or its allyl carbonate analogue are ionized under Pd catalysis to generate the 2-bromo Pd-pi-allyl complex (triphenylphosphine ligand), which alkylates with malonate nucleophile at the terminal position. The presence of acetate ion in the reaction mixture results in some malonate attack being redirected to the central carbon. The acetate ion can come from the ionization of 1-acetoxy-2-bromo-2-propene or by the addition of silver acetate to the reaction mixture. The addition of phenoxide ion to the reaction also causes the same regiochemical phenomena, although harder anions such as methoxide exert no such effect.

Solid-phase synthesis of a tyrphostin ether library.

The solid-phase synthesis of a 4500-member (30 x 15 x 10) tyrphostin library is demonstrated utilizing the Irori-directed sorting system. Fmoc-protected PL-Rink resin was used as the solid support. After Fmoc-deprotection, aryl aldehydes were attached to the resin through reductive amination. Acylation of the resulting secondary amines with cyanoacetic acid was followed by a Knoevenagel condensation with phenolic aldehydes. Mitsunobu coupling of primary alcohols to the resin-bound phenols yielded the final library of compounds 1.

Solid-Phase Synthesis of 2,4-diaminopyrimidines via Lewis acid-mediated aromatic nucleophilic substitution.

Primary amines were immobilized on (4-formyl-3,5-dimethoxyphenoxy)methylpolystyrene resin via reductive amination. Attachment of two different 4-chloro-2-methylthiopyrimidines, followed by sulfide oxidation, led to their corresponding sulfone intermediates. Aromatic nucleophilic substitution with various anilines or heteroaromatic amines in the presence of trimethyl aluminum afforded the desired 2,4-diaminopyrimidines after acidic cleavage from the resin. The synthetic methodology described herein was validated with the synthesis of a small 162-member library.

Controlling chemoselectivity in vinyl and allylic C-X bond activation with palladium catalysis: a pK(a)-based electronic switch.

It has been demonstrated that the same Pd catalyst can be used to effect allylic substitution or vinylic cross-coupling reactions selectively and interchangeably on polyfunctionalized olefin building blocks despite the differences in reaction mechanism. This was achieved by altering the pK(a) of the conjugate acid of the allylic leaving group while keeping the vinyl coupling partner constant. In the case of 2,3-dibromo-1-propene, Pd-catalyzed allylic ionization with malonate nucleophile proceeded selectively and quantitatively in the presence of the Suzuki reaction components necessary for cross-coupling. Conversely, the bromide of 2-bromo-1-(4-ethylphenoxy)-2-propene could be cross-coupled selectively without activation of the allylic phenoxy substituent. In both reactions, the same catalyst could then be used to complete the sequence, which typically involved heating as the trigger to promote the second, more reluctant reaction. Mechanistic considerations as well as synthetic applications demonstrating the value of this interchangeable catalyzed sequence are presented.