Synthèse d'alkyl-2- tétrahydro-2,3,6,7 oxépinnes et oxocinnes à partir d'allylsilanes

Iron-Catalyzed Prins-Peterson Reaction for the Direct Synthesis of Δ4-2,7-Disubstituted Oxepenes

A direct iron(III)-catalyzed Prins-Peterson reaction involving α-substituted γ-triphenylsilyl bis-homoallylic alcohols and aldehydes is described. Thus, cis-Δ⁴-2,7-disubstituted oxepenes were synthesized in a diastereoselective reaction using sustainable catalytic conditions (3-5 mol %). This highly productive process is the result of a cascade of three chemical events with the concomitant formation of a C-O bond, a C-C bond, and a Δ⁴ endocyclic double bond, through a Prins cyclization followed by a Peterson-type elimination. This tandem reaction is chemoselective vs the classical Prins cyclization.

An Efficient Synthesis of Benzazocines by Gold(I)-Catalyzed Tandem 1,2-Acyloxy Shift/[3+2] Cycloaddition of Terminal 1,9-Enynyl Esters

An effective synthesis of structurally diverse benzazocines was accomplished in good to excellent chemical yields (55-82 %) through a gold(I)-catalyzed cascade reaction involving tandem 1,2-acyloxy shift/[3+2] cycloaddition of terminal 1,9-enynyl esters. The reaction proceeds under extremely mild conditions and represents one of the relatively few transition-metal-catalyzed intramolecular cycloaddition reactions for the synthesis of benzazocines.

Stereoselective Synthesis of Substituted Oxocene Cores by Lewis Acid Promoted Cyclization

Substituted oxocene derivatives have been synthesized by Lewis acid catalyzed reactions of ε-hydroxyalkene and substituted aromatic aldehydes. The Cu(OTf)2-bis-phosphine catalyzed reaction typically provides substituted dihydropyran derivatives through an olefin migration followed by a Prins cyclization. The corresponding reaction catalyzed by TMSOTf or BF3·OEt2 provided eight-membered cyclic ethers (oxocenes), selectively. This methodology provides convenient access to a variety of 2,4,8-trisubstituted oxocenes in good yields and excellent diastereoselectivities.

Electron Transfer Photochemistry of Homochrysanthemol: Intramolecular Nucleophilic Attack on the Cyclopropane Ring

The electron-transfer photochemistry of homochrysanthemol, 1, resulted exclusively in intramolecular "substitution" at the quaternary cyclopropane carbon, generating the five-membered cyclic ethers, 2 and 4. The alternative "addition" to the terminal carbon of the double bond, which would result in seven-membered cyclic ethers, 3 and 5, was not observed. Apparently, the five-membered transition state leading to 2 and 4 is significantly favored over the seven-membered one required for formation of 3 and 5. These results stand in interesting contrast to the previously established reaction pattern of chrysanthemol, 8, which is captured exclusively at the terminal vinyl carbon. The divergent regiochemistry of 1(*)(+) and 8(*)(+) (even though the tethers between vinylcyclopropane and alcohol functions differ only by a single CH(2) group) elucidates the principles governing the course of nucleophilic capture in radical cations.