Synthesis of 1,4-diketones
A Ru2+-photocatalyzed, visible-light-mediated ATRA reaction of α-bromoketones with alkyl enol ethers provides 1,4-ketoaldehydes, 1,4-diketones, and 1,4-ketoesters, which are difficult to access. This method enables the construction of secondary, tertiary, and challenging quaternary centers. A construction of substituted pyrroles is also described.
W. H. García-Santos, H. B. Mateus-Ruiz, A. Cordero-Vargas, Org. Lett., 2019, 21, 4092-4096.
Dibrominated 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is an organic photocatalyst with similar optoelectronic, electrochemical, and performance properties to those of Ru(bpy)3Cl2, commonly used in radical-ionic transformation, such as the formation of 1,4-dicarbonyl compounds. BODIPY also catalyzes syntheses of γ-alkoxylactones, monoprotected 1,4-ketoaldehydes, and dihydrofurans.
W. H. García-Santos, J. Ordóñez-Hernández, M. Farfán-Paredes, H. M. Castro-Cruz, N. A. Macías-Ruvalcaba, N. Farfán, A. Cordero-Vargas, J. Org. Chem., 2021, 86, 16315-16326.
A visible-light-induced radical coupling reaction of silyl enol ethers with α-bromocarbonyl compounds provides 1,4-dicarbonyls. The reaction was effectively accelerated using an inexpensive organic dye (eosin Y) as a photoredox catalyst.
N. Esumi, K. Suzuki, Y. Nishimoto, M. Yasuda, Org. Lett., 2016, 18, 5704-5707.
A silver-catalyzed controlled intermolecular cross-coupling of silyl enolates displays good functional group tolerance and allows efficient preparation of a series of synthetically useful 1,4-diketones. Preliminary mechanistic investigations suggest that the reaction proceeds through a one-electron process involving free radical species in which PhBr acts as the oxidant.
L. Xu, X. Liu, G. R. Alvey, A. Shatskiy, J.-Q. Liu, M. D. Kärkäs, X.-S. Wang, Org. Lett., 2022, 24, 4513-4518.
In a Co-catalyzed reaction for the construction of 1,4-dicarbonyls, a cascade organocobalt addition/trapping/Kornblum-DeLaMare rearrangement were involved. The reaction offers easy availability of starting materials, wide substrate scope, high functionality tolerance, and operational simplicity.
F. Zhang, P. Du, J. Chen, H. Wang, Q. Luo, X. Wan, Org. Lett., 2014, 16, 1932-1935.
The perovskite colloid CsPbBr3 can selectively photocatalyze α-alkylation of aldehydes with a turnover number (TON) of over 52,000 under visible light illumination.
X. Zhu, Y. Lin, Y. Sun, M. C. Beard, Y. Yan, J. Am. Chem. Soc., 2019, 141, 733-738.
Singly occupied molecular orbital (SOMO) catalysis allows an enantioselective organocatalytic α-enolation of aldehydes. A chiral secondary amine catalyst reacts with aldehydes to form transient enamines that undergo selective one-electron oxidation to generate SOMO-activated electrophilic radical cations which are susceptible to attack by ketone-derived enol silanes.
H.-Y. Jang, J.-B. Hong, D. W. C. MacMillan, J. Am. Chem. Soc., 2007, 129, 7004-7005.
A tandem reaction consisting of a Wittig reaction-ring contraction process between α-hydroxycyclobutanone and phosphonium ylides provides highly functionalized cyclopropanecarbaldehydes in very good yield.
F. Cuccu, L. Serusi, A. Luridiana, F. Secci, P. Caboni, D. J. Aitken, A. Frongia, Org. Lett., 2019, 21, 7755-7758.
CuO catalyzes a three-component reaction of α-ketoaldehydes, 1,3-dicarbonyl compounds, and organic boronic acids in water to provide a wide range of products containing 1,3- and 1,4-diketones. The method offers use of readily available starting materials, wide substrate scope, excellent yields, gram-scale synthesis, and mild reaction conditions.
Q. Xia, X. Li, X. Fu, Y. Zhou, Y. Peng, J. Wang, G. Song, J. Org. Chem., 2021, 86, 9914-9923.