Six‐ and Eightfold Palladium‐Catalyzed Cross‐Coupling Reactions of Hexa‐ and Octabromoarenes

Abstract

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 1 a and 1 i, making them nicely cup-shaped molecules, or alternatingly above and below the central plane as in 1 h 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, 1 a 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 (3 b, 62 % yield), 1-ethynyl-1-methylcyclohexane (3 c, 85 %) and 3,3-dimethylpentyne (3 e, 65 %). 1-(Trimethylsilyl)ethynylcyclopropane (7) was used to prepare 1-ethynyl-1-methylcyclopropane (3 d) (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).

Insight into the structures of [M(C5H4I)(CO)3] and [M2(C12H8)(CO)6] (M= Mn and Re) containing strong I...O and π(CO)–π(CO) interactions

“…Examples include dendrimers (Tomalia et al, 1990;Stulgies et al, 2005;Astruc et al, 2008), staffanes (Kaszynski et al, 1992), Diederich's carbon nets (Diederich & Rubin, 1992), and various novel electronic, photonic and magnetic materials (Barlow & O'Hare, 1997;Elschenbroich et al, 2005;Kinnibrugh et al, 2009). Because of the increasing interest in this area, we have focused our studies on structural investigations of the title compounds, (I)-(IV) (Figs.…”

Cross‐Coupling of Organyl Halides with Alkenes: the Heck Reaction

“…This reaction mode plays a dominant role in the attempted six-fold Heck coupling of hexabromobenzene with styrenes yielding complex mixtures of various isomers of the six-fold coupling product. The analogous six-fold Suzuki and Stille coupling reactions with alkenylboronates and alkenylstannanes, respectively, gave the corresponding pure hexakisalkenylbenzene derivatives in high yields [264,265]. Even an eight-fold Suzuki coupling of octabromonaphthalene with an alkenylboronate has recently been achieved [265].…”

“…The analogous six-fold Suzuki and Stille coupling reactions with alkenylboronates and alkenylstannanes, respectively, gave the corresponding pure hexakisalkenylbenzene derivatives in high yields [264,265]. Even an eight-fold Suzuki coupling of octabromonaphthalene with an alkenylboronate has recently been achieved [265]. 237 …”

Peralkynylated Tetraazaacene Derivatives

“…It was obtained by ac ombination of condensation reactions giving the two pyraziner ings and subsequentc onsecutive Stille-type couplings. [7] To solve this issue, the offending peri interactions will have to be removedb ys ubstitution of aC -CC-R-group throughanitrogen. The presence of the four nitrogen atomsr emoves the peri interaction of the substituted alkyne groups, giving this rock-stable and highly twisted heteroacene.…”

“…Peralkynylated representatives are known of some aromatic systems;t he first ever described was Vollhardt's hexaethynylbenzene, prepared from hexabromobenzene and TMS acetylene in as ixfold Sonogashira reaction. [7] To solve this issue, the offending peri interactions will have to be removedb ys ubstitution of aC -CC-R-group throughanitrogen. [6] However,f or larger aromatic systems, such as naphthalene or anthracene, peralkynylated species are unknown-attempts of alkynylation lead to annulation reactions due to severe peri interactions of the alkynes-yet ap eralkenylated naphthalene has been prepared by de Meijere and co-workers.…”