A cobalt-catalyzed neutral Diels-Alder reaction of dienes derived from aldehydes with terminal and internal alkynes, and DDQ oxidation of the dihydroaromatic intermediates leads to regiochemically enriched biphenyl, terphenyl, and silyl-functionalized benzene derivatives in good to excellent yields.
G. Hilt, M. Danz, Synthesis, 2008, 2257-2263.
The cobalt-catalyzed Diels-Alder reaction of alkynyl pinacol boronic esters with various dienes generates cycloadducts in very good regioselectivity. A reaction sequence (Diels-Alder reaction, Suzuki coupling, DDQ oxidation) was successfully performed as a one pot operation without isolation of the intermediates.
G. Hilt, K. I. Smolko, Angew. Chem. Int. Ed., 2003, 42, 2795-2797.
Intramolecular carbonyl allylation of α-prenyl β-arylketosulfones in the presence of molecular sieves affords substituted benzenes in good yields via Bi(OTf)3-mediated annulation followed by a sequential desulfonative aromatization. The use of α-geranyl β-arylketosulfones enables the synthesis of tetrahydronaphthalenes.
M.-Y. Chang, Y.-C. Cheng, Y.-J. Lu, Org. Lett., 2015, 17, 3142-3145.
DBU mediates a [2 + 4] annulation of in situ activated α,β-unsaturated carboxylic acids and α-cyano-β-methylenones to provide 1,3,5-trisubstituted benzenes. The dual role of DBU as Brønsted base and nucleophilic Lewis base is the key for the success of the reaction.
C.-L. Zhang, Z.-F. Zhang, Z.-H. Xia, Y.-F. Han, S. Ye, J. Org. Chem., 2018, 83, 12507-12513.
A N-heterocyclic carbene-catalyzed [2 + 4] annulation of α-bromoenals and α-cyano-β-methylenones enables a direct and efficient approach to 1,3,5-trisubstituted benzenes. The reaction worked well for both aryl- and alkylenones.
C.-L. Zhang, S. Ye, Org. Lett., 2016, 18, 6408-6411.
An efficient base-catalyzed [3 + 3] oxidative aromatization of α,β-unsaturated carbonyl compounds with dimethyl glutaconate under mild, metal-free conditions affords substituted benzenes in high to excellent yields with oxygen as oxidant and water as sole byproduct. In situ generation of the α,β-unsaturated carbonyl compounds from aldehydes and ketones enables a more convenient tandem [3 + 2 + 1] aerobic oxidative aromatization reaction.
A. Diallo, Y.-L. Zhao, H. Wang, S.-S. Li, C.-Q. Ren, Q. Liu, Org. Lett., 2012, 14, 5776-5779.
Salicylic acid derivatives were prepared by Me3SiOTf-catalyzed [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 1,1,3,3-tetramethoxypropane under mild conditions in moderate yields.
M. Sher, T. H. T. Dang, Z. Ahmed, M. A. Rashid, C. Fischer, P. Langer, J. Org. Chem., 2007, 72, 6284-6286.
Various substituted phenol and benzene derivatives were prepared through RCM-tautomerization and RCM-dehydration protocols without formation of inseparable regioisomers.
K. Yoshida, S. Horiuchi, N. Iwadate, F. Kawagoe, T. Imamoto, Synlett, 2007, 1561-1562.
A ring-closing olefin metathesis (RCM)/elimination sequence or an RCM/tautomerization sequence of functionalized pyrrole precursors enabled the selective synthesis of substituted indoles. The RCM/elimination sequence was also applied to double ring closure to yield a substituted carbazole.
K. Yoshida, K. Hayashi, A. Yanagisawa, Org. Lett., 2011, 13, 4762-4765.
A AuCl-catalyzed, flexible synthesis of highly substituted, benzyl-protected phenols unites enal/enones and benzyl allenyl ethers in a [3+3] fashion in two steps, allowing excellent control of substitution at the benzene ring.
X. Huang, L. Zhang, Org. Lett., 2007, 9, 4627-4630.
A gold(I)-catalyzed intramolecular hydroarylation of (Z)-2-(enynyl)indoles gives carbazoles in good yields. The requisite (Z)-2-(enynyl)indoles were synthesized stereoselectively by trimethylgallium-promoted, Z-selective Wittig olefination of N-alkylindole-2-carboxaldehydes with propargyl ylides.
C. Praveen, P. T. Perumal, Synlett, 2011, 268-272.
A cationic rhodium(I)/BINAP complex-catalyzed decarboxylative [2 + 2 + 2] cycloaddition of 1,6- and 1,7-diynes with commercially available vinylene carbonate enables a new route to substituted phenols.
H. Hara, M. Hirano, K. Tanaka, Org. Lett., 2009, 11, 1337-1340.