A Facile Diels−Alder Reaction with Benzene:  Synthesis of the Bicyclo[2.2.2]octene Skeleton Promoted by Rhenium

A Diels–Alder super diene breaking benzene into C2H2 and C4H4 units

“…Only a limited number of examples of the Diels–Alder reaction involving benzene derivatives have been reported1011121314151617. The limited reactivity of this π system is because of the enormous stability afforded by aromaticity, which can only be overcome under certain conditions18.…”

“…The limited reactivity of this π system is because of the enormous stability afforded by aromaticity, which can only be overcome under certain conditions18. Currently, there are only a limited number of options to activate benzene sufficiently, including coordination of a transition metal complex to benzene10, naphthalene with small resonance energy11 and the use of benzene derivatives with a sterically induced strained geometry121314. Alternatively, exceptionally strong dienophiles or dienes under severe conditions (for example, high temperature and pressure) will undergo Diels–Alder cyclization with benzene15161718192021, and reactive unsaturated heavier main group analogues of an alkene or alkyne make adducts with arenes under mild conditions222324.…”

Asymmetric organic synthesis with stoichiometric transition metal complexes

“…48,49 Early studies from Harman's group reported cycloadditions of η 2 -coordinated Re complexes of benzene and N-methyl pyrrolidine with reactive dienophiles to afford organic products with bicyclo[2.2.2]octane or heterocyclic bicyclo[2.2.1]heptane skeletons (Scheme 27). 50 A pair of impressive studies on dearomatization of phenol via η 2 -coordination with W uncovered a regio-and stereoselective [2+2] reaction of the W complexes of phenol with ketene, 51 as well as a series of selective bis-functionalizations of the complexed phenol to afford cis-4,5-disubstitued cyclohex-2-en-1-ones (Scheme 27). 52…”

Dearomatizing and Derivatizing a Mesityl Group on Boron by One‐Pot Photoisomerization and [4+2] Diels–Alder Addition

“…[5b] 2 (22 mg, 51 mmol) was dissolved in C 6 D 6 (2 mL, c = 0.025 m)a nd irradiated with UV light at 365 nm for 7days to fully convert it into 2a.D MAD (0.1 mL, 0.82 mmol) was then added in as ingle portion to the solution of 2a.A fter heating overnight in an oil bath at 30 8C, the clear yellow solution containing the product was concentrated in vacuo and purified by column chromatography on neutral alumina eluting with hexanes/ ethyl acetate (9:1), affording ay ellow residue of 2b.C rystals of 2b were grown by slow evaporation of the volatiles from ac oncentrated solution in hexanes/ethyl acetate (5:1) and washed with hexanes to afford the pure compound (28 mg, 94 %). 1 HNMR (700 MHz, C 6 D 6 ): d = 9.23 (d,J = 8.5 Hz,1H; : d = 169.90, 165.83, 162.79, 159.64, 148.53, 147.59, 141.03, 140.90, 137.40, 136.92, 134.74, 134.31, 132.22, 131.16, 129.04, 128.20, 128.06, 127.92, 127.10, 123.90, 123.17, 54.65, 52.50, 51.87, 51.44, 23.90, 23.89, 21.30, 20.32, 20.27, 16.33, 11.15 Synthesis of 3b:Compound 3 was synthesized according to aprevious literature procedure. [5c] Compound 3 (4.0 mg, 9 mmol) was solubilized in C 6 D 6 (0.51 mL, c = 0.017 m)a nd irradiated with UV light at 300 nm for 3h to fully convert it into 3a.D MAD (0.1 mL, 0.82 mmol) was then added to the reaction mixture in asingle portion.…”