We report a general palladium-catalyzed b-arylation of Boc-piperidines, which yields a variety of valuable 3-arylpiperidines in a simple and direct manner. The b-vs. a-arylation selectivity was controlled by the ligand, with flexible biarylphosphines providing mainly the desired b-arylated products whereas more rigid biarylphosphines mainly furnished the more classical a-arylated products. The computed reaction mechanism (DFT), studied from the common a-palladated intermediate, indicated that the reductive elimination steps leading to the aand b-arylated products are selectivitydetermining. Moreover, the experimental trend obtained with different ligands was well reproduced by the calculations.
A new class of strigolactone analogues has been synthesized. They differ from known molecules, both of natural and synthetic origin, in two main features. The conjugated system extends from the enol ether bridge to the A ring, the B ring is a heterocycle while the C ring is a cyclic ketone instead of a g-lactone. The key step of the synthesis is a Nazarov cyclization on activated substrates. Bioassays using Orobanche seeds have revealed that all the molecules strongly stimulate germination; in particular the oxygen containing analogues are the most active. Interestingly, some of the new molecules show fluorescent properties.
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