193755-69-0Relevant academic research and scientific papers
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).
