21079-27-6Relevant articles and documents
-
Cordes,C. et al.
, p. 1663 - 1678 (1968)
-
Remote Cooperative Group Strategy Enables Ligands for Accelerative Asymmetric Gold Catalysis
Wang, Zhixun,Nicolini, Corrado,Hervieu, Cedric,Wong, Yuk-Fai,Zanoni, Giuseppe,Zhang, Liming
supporting information, p. 16064 - 16067 (2017/11/22)
An accelerative asymmetric gold catalysis is achieved for the first time via chiral ligand metal cooperation. An asymmetrically positioned remote amide group in the designed chiral binaphthyl-based ligand plays the essential role of a general base catalyst and selectively accelerates the cyclizations of 4-allen-1-ols into one prochiral allene face. The reactions are mostly highly enantioselective with achiral substrates, and due to the accelerated nature of the catalysis catalyst loadings as low as 100 ppm are allowed. With a pre-existing chiral center at any of the backbone sp3-carbons, the reaction remained highly efficient and most importantly maintained excellent allene facial selectivities regardless of the substrate stereochemistry. By using different combinations of ligand and substrate enantiomers, it is now possible to access all four stereoisomers of versatile 2-vinyltetrahydrofurans with exceedingly high selectivity. The underpinning design of this chemistry reveals a novel and conceptually distinctive strategy to tackle challenging asymmetric gold catalysis, which to date has relied on decelerative asymmetric steric hindrance approaches.
Six- and eightfold palladium-catalyzed gross-coupling reactions of hexa- and octabromoarenes
Stulgies, Balder,Prinz, Peter,Magull, Joerg,Rauch, Karsten,Meindl, Kathrin,Ruehl, Stephan,De Meijere, Armin
, p. 308 - 320 (2007/10/03)
Palladium-catalyzed sixfold coupling of hexabromobenzene (20) with a variety of alkenylboronates and alkenylstannanes provided hexaalkenylbenzenes 1 in up to 73% and 16 to 41% yields, respectively. In some cases pentaalkenylbenzenes 21 were isolated as the main products (up to 75%). Some functionally substituted hexaalkenylbenzene derivatives containing oxygen or sulfur atoms in each of their six arms have also been prepared (16 to 24% yield). The sixfold coupling of the less sterically encumbered 2, 3, 6, 7, 10, 11-hexabromotriphenylene (24) gave the desired hexakis(3,3-dimethyl-1-butenyl) triphenylene (25) in 93% yield. The first successful cross-coupling reaction of octabromonaphthalene (26) gave octakis-(3,3-dimethyl-1-butenyl)naphthalene (27) in 21% yield. Crystal structure analyses disclose that, depending on the nature of the substituents, the six arms are positioned either all on the same side of the central benzene ring as in 1a and 1i, making them nicely cup-shaped molecules, or alternatingly above and below the central plane las in 1h and 23. In 27, the four arms at C-1, 4, 6, 7 are down, while the others are up, or vice versa. Upon catalytic hydrogenation, 1a yielded 89% of hexakis(tert-butylethyl)benzene (23). Some efficient accesses to alkynes with sterically demanding substituents are also described. Elimination of phosphoric acid from the enol phosphate derived from the corresponding methyl ketones gave 1-ethynyladamantane (3b, 62% yield), 1-ethynyl-1-methylcyclohexane (3c, 85%) and 3,3-dimethylpentyne (3e, 65%). 1-(Trimethylsilyl)ethynylcyclopropane (7) was used to prepare 1-ethynyl-1-methylcyclopropane (3d) (two steps, 64% overall yield). The functionally substituted alkynes 3 f-h were synthesized in multistep sequences starting from the propargyl chloride 11, which was prepared in high yields from the dimethylpropargyl alcohol 10 (94%). The alkenylstannanes 19 were prepared by hydrostannation of the corresponding alkynes in moderate to high yields (42-97%), and the alkenylboronates 2 and 4 by hydroboration with catecholborane (27-96% yield) or pinacolborane (26-69% yield).
