Palladium-Catalyzed Synthesis of 1-Alkylidene-2-dialkylaminomethyl Cyclobutane Derivatives via Pd-Catalyzed Alkene Difunctionalization Reactions: Influence of Nucleophile and Water on the Reaction Mechanism.

The Pd-catalyzed coupling of 1,5-diene-2-yl triflates with amine nucleophiles affords exomethylenecyclobutanes bearing dialkylaminomethyl groups at C2. The strained carbocyclic products are obtained in moderate to excellent yields, with regioselectivities of up to >95:5 for four-membered ring formation. The mechanism of these reactions, which provides products resulting from anti-addition to alkenes, differs from related reactions involving malonate nucleophiles that provide syn-addition products.

Regiodivergent Palladium-Catalyzed Alkene Difunctionalization Reactions for the Construction of Methylene Cyclobutanes and Methylene Cyclopentanes.

Regiodivergent palladium-catalyzed alkene difunctionalization reactions between diethyl malonate and 1,5-dienes bearing a triflate group at C2 are described. Use of tris(2,4-di-tert-butylphenyl)phosphite as a ligand leads to 4-exo-cyclization/functionalization to afford malonate-substituted methylene cyclobutanes. In contrast, the 1,2-bis(diphenylphosphino)benzene ligand provides methylene cyclopentanes via 5-endo-cyclization/functionalization. The five-membered ring-forming reactions occur via anti-carbopalladation of the enolate nucleophile, whereas four-membered ring-forming reactions proceed through syn-4-exo-migratory insertion of the tethered alkene, followed by C(sp3)-C(sp3) bond-forming reductive elimination from an (alkyl)Pd(II)(malonate) complex.

Glycosyl Exchange of Unactivated Glycosidic Bonds: Suppressing or Embracing Side Reactivity in Catalytic Glycosylations.

While developing boron-catalyzed glycosylations using glycosyl fluoride donors and trialkylsilyl ether acceptors, competing pathways involving productive glycosylation or glycosyl exchange were observed. Experimental and computational mechanistic studies suggest a novel mode of reactivity where a dioxolenium ion is a key intermediate that promotes both pathways through addition to either a silyl ether or to the acetal of an existing glycosidic linkage. Modifications in catalyst structure enable either pathway to be favored, and with this understanding, improved multicomponent iterative couplings and glycosyl exchange processes were demonstrated.

Silanediol Anion Binding and Enantioselective Catalysis.

Silanediols possess unique and complementary catalytic activity in reactions that are likely to proceed through anion binding. This article directly compares silanediols, thioureas, and squaramides in three separate anion-binding processes. The catalytic abilities of select members of each family are directly correlated to association constant.