Regioselective Silane-Terminated Intramolecular Heck Reaction with Alkenyl Triflates and Alkenyl Iodides

Synthesis of Sulfur-Containing Exo-Bicyclic Dienes and Their Diels-Alder Reactions To Access Thiacycle-Fused Polycyclic Systems

The stereocontrolled synthesis of unprecedented sulfur-containing exo-bicyclic 1,3-dienes is reported through a palladium-catalyzed reductive cyclization of sulfur-linked 2-bromoenynes. The fused bicyclic structure provides a better stability to the thiacyclic diene compared to the simple 3,4-dimethylenetetrahydrothiophene. Their reactivity toward several dienophiles has been investigated, and various original thiacycle-fused polycyclic systems have been obtained with high or total diastereoselectivity. Moreover, they are the first exo-bicyclic dienes used in Diels-Alder reactions. The relative configurations of four cycloadducts have been unambiguously assigned by X-ray crystallographic analysis. Mechanistic details of the cycloadditions have been examined by computational means.

Enantioselective carbocycle formation through intramolecular Pd-catalyzed allyl-aryl cross-coupling

Aryl electrophiles containing tethered allylboronate units undergo efficient intramolecular coupling in the presence of a chiral palladium catalyst to give enantioenriched carbocyclic products. The reaction is found to be quite general, affording 5, 6, and 7-membered carbocyclic products as single regioisomers and with moderate enantioselectivities. Examination of differential coupling partners points to rapid allyl-equilibration as a key stereodefining feature.

Efficient synthesis of tetrasubstituted alkenes by allylsilane-terminated domino-Heck double cyclisation

The domino-Heck double cyclisation of the arylbromides 1, which contain an allylsilane and an alkyne moiety and are easily accessible by an addition of the corresponding lithiated alkynes 5 to the aldehydes 4, leads to the tetrasubstituted alkenes 2 and 3 in good yield. The reaction produces exclusively compounds with an E double bond and additionally proceeds with good to excellent induced diastereoselectivity in the case of 1e and 1f. Irradiation of 2e leads to a steady state equilibrium of the E and Z compounds in a 1:1 ratio.