The oxyallyl cation intermediate from the Lewis acid mediated Nazarov reaction of an allenyl vinyl ketone was intercepted by acyclic, 2-silyloxy-substituted butadienes by highly regioselective (4 + 3) cycloadditions. Stereoselectivity was often modest, but in some instances steric interactions were responsible for high selectivity. The results are consistent with concerted (4 + 3) cycloadditions. In many instances, the (4 + 3) products were susceptible to fragmentation or rearrangement in the presence of the Lewis acid.
The competitive catalytic screening of 18 known and newly prepared Mor-DalPhos ligand variants in the palladium-catalyzed cross-coupling of chlorobenzene with aniline, octylamine, morpholine, indole, ammonia, or acetone is presented, including ligands derived from the new secondary phosphine HP(Me2Ad)2 (Me2Ad = 3,5-dimethyladamantyl). Although triarylphosphine ancillary ligand variants performed poorly in these test reactions, ligands featuring either PAd2 or P(Me2Ad)2 donors (Ad = 1-adamantyl) gave rise to superior catalytic performance. Multiple Mor-DalPhos variants proved effective in cross-couplings involving aniline, octylamine, or morpholine; conversely, only a smaller subset of ligands proved useful in related cross-couplings of indole, ammonia, or acetone. In the case of the N-arylation of indole, a Mor-DalPhos ligand variant featuring ortho-disposed PAd2 and dimethylmorpholino donor fragments (L13) proved superior to all other ligands surveyed, including the parent ligand Mor-DalPhos (L5). Conversely, L5 was found to be superior to all other ligands in the palladium-catalyzed monoarylation of ammonia. Ligand L6 (i.e., the P(Me2Ad)2 variant of L5) proved superior to all other ligands in the monoarylation of acetone and, with the exception of indole N-arylation, was the most broadly useful of the Mor-DalPhos ligands surveyed herein.
Nazarov reactions Intercepted by (4 + 3) Cycloadditions with Oxygen-SubstitutedDienes. -An oxyallyl cation, generated by Nazarov reaction of an allenyl vinyl ketone, is trapped by regioselective cycloaddition with 2-siloxy-1,3-butadienes to give bicyclo[4.2.1]nonane derivatives. -(LEFORT, F. M.; MISHRA, V.; DEXTER, G. D.; MORGAN, T. D. R.; BURNELL*, D. J.; J. Org. Chem. 80 (2015) 11, 5877-5886, http://dx.doi.org/10.1021/acs.joc.5b00914 ; Dep. Chem., Dalhousie Univ., Halifax, Nova Scotia B3H 4R2, Can.; Eng.) -T. Stabingis 43-077
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