Organocatalyzed C-C Ring Construction: The Takao Synthesis of Puraquinonic Acid

Xiaoxia Ye of Wenzhou Medical University and Jun Jiang of Wenzhou University used the barium salt of proline to direct the aldol reaction of the prochiral cyclobutanone 1 with the α-ketoester 2, leading to the diester 3 (Synlett 2022, 33, 1619. DOI: 10.1055/s-0040-1719931). Rong-Jie Chein of the Academia Sinica used a oxathiaborolium catalyst to mediate the [2+2] cycloaddition of the silyl enol ether 4 with the maleimide 5, to give the cyclobutane 6 (Org. Biomol. Chem. 2022, 20, 8405. DOI: 10.1039/D2OB01779B).

David A. Nicewicz of the University of North Carolina employed an acridinium photocatalyst to cyclize the aldehyde 7 to the cyclopentanol 8 (J. Am. Chem. Soc. 2022, 144, 11888. DOI: 10.1021/jacs.2c04822). Jisheng Luo and Li Deng of Westlake University used a bisphosphine catalyst to set the absolute configuration of the conjugate addition of the imine 10 to cyclopentenone 9, leading to 11 (J. Am. Chem. Soc. 2022, 144, 23264. DOI: 10.1021/jacs.2c10777). Aijun Lin and Hequan Yao of China Pharmaceutical University showed that a BINOL-derived phosphoric acid was effective for cyclizing the prochiral epoxide 12 to the bicyclic amine 13 (Org. Lett. 2022, 24, 8791. DOI: 10.1021/acs.orglett.2c03529). Baomin Wang of the Dalian University of Technology used a Cinchona-derived catalyst to construct the cyclopentadiene 16 by the combination of the carbonate 14 with the alkynyl ketone 15 (Chem. Commun. 2022, 58, 9504. DOI: 10.1039/D2CC02963D).

Giovanni Piersanti of the University of Urbino Carlo Bo used a diamine-derived thiourea to catalyze the addition of cyclohexanone 17 to the dehydroalanine 18, leading to the amine 19 in high ee (Chem. Eur. J. 2022, 28, e202201994. DOI: 10.1002/chem.202201994). María de Gracia Retamosa of the Universidad de Alicante and Fernando P. Cossio of the University of the Basque Country showed that a γ-dipeptide effectively catalyzed the addition of cyclohexanone 17 to the nitrodiene 20 to give, after the addition of ethyl glyoxylate 21, the ester 22 (J. Org. Chem. 2022, 87, 14819. DOI: 10.1021/acs.joc.2c01230). Xiaochuan Chen of Sichuan University used DMAP to cyclize the dialdehyde 23 to the cyclohexanol 24 (J. Org. Chem. 2022, 87, 14636. DOI: 10.1021/acs.joc.2c01992). Jeremy A. May of the University of Houston employed a BINOL derivative to mediate the enantioselective conjugate addition of the trifluoroborate 26 to the dienone 25, leading after intramolecular aldol condensation to the 5-substituted cyclohexenone 27 (Org. Lett. 2022, 24, 5334. DOI: 10.1021/acs.orglett.2c01976).

Anthony P. Green of the University of Manchester designed a photocatalytic enzyme that directed the cyclization of the diene 28 to the cyclobutane 29 (Nature 2022, 611, 709. DOI: 10.1038/s41586-022-05335-3). Manabu Hatano of Kobe Pharmaceutical University and Kazuaki Ishihara of Nagoya University used a BINOL-derived phosphoric acid enhanced by BBr₃ to mediate the Diels-Alder addition of the unsaturated aldehyde 30 to cyclopentadiene, leading, after acid-mediated ring expansion, to the tetracyclic ketone 31 (Org. Lett. 2022, 24, 6483. DOI: 10.1021/acs.orglett.2c02747).

Puraquinonic acid 35, produced by cultures of the fungus Mycena pura, induces differentiation of HL-60 cells (human promyelocytic leukemia) and may therefore be a lead compound in the design of drugs to treat leukemia. En route to 35, Ken-ichi Takao of Keio University added the alkyne 33 to the Oppolzer acryloylsultam 32, leading to the monoester 34 in high ee (J. Org. Chem. 2022, 87, 8788. DOI: 10.1021/acs.joc.2c00753).