Organocatalyzed C-C Ring Construction: The Sattely Synthesis of Momilactone

Arnaud Voituriez of the Université Paris-Saclay used a cyclic phosphine to mediate the assembly of the cyclobutene 3 by the addition of the β-diketone 1 to the acetylene dicarboxylate 2 (Adv. Synth. Catal. 2021, 363, 4805. DOI: 10.1002/adsc.202100664). Xiao-Chen Wang of Nankai University showed that a bis-borane catalyst effected both alkene migration and addition to the alkynyl ketone 5, leading to the cyclobutene 6 (Angew. Chem. Int. Ed. 2021, 60, 17185. DOI: 10.1002/anie.202106168).

Natsuhisa Oka and Kaori Ando of Gifu University rearranged the nucleoside-derived tetrazole 7 to the cyclopentene 8 (J. Org. Chem. 2021, 86, 16684. DOI: 10.1021/acs.joc.1c01940). Yixin Lu of the National University of Singapore used an amidophosphine to promote the addition of the oxindole 9 to the allenyl ketone 10, leading to the cyclopentene 11 (Org. Chem. Front. 2021, 8, 4485. DOI: 10.1039/D1QO00669J). Qijian Ni and Xiaoxiao Song of Anhui Normal University showed that a chiral phosphoric was directed the conjugate addition of the indolizine 13 to the prochiral diketone 12, to give 14 (Org. Lett. 2021, 23, 9548. DOI: 10.1021/acs.orglett.1c03780). Yi Tang of UCLA employed a cell-free enzyme complex to convert geraniol 15 to the important insect repellent nepetalactone 16 (ACS Catal. 2021, 11, 9898. DOI: 10.1021/acscatal.1c02267).

Yu-Fei Ao of the Institute of Chemistry of the Chinese Academy of Sciences used a modified strain of E. coli to selectively hydrolyze the prochiral bisamide 17, leading to the monoester 18 (Adv. Synth. Catal. 2021, 363, 4538. DOI: 10.1002/adsc.202100597). Masahiro Terada of Tohoku University used a chiral bisphosphoric acid in combination with a boronic acid to cyclize the prochiral tertiary alcohol 19 to the corresponding spiro epoxide, that was further rearranged to the cyclohexanone 20 (Tetrahedron 2021, 98, 132412. DOI: 10.1016/j.tet.2021.132412). Gonghua Song and Jinxing Ye of the East China University of Science and Technology showed that with a diamine catalyst, addition of the deconjugated cyclohexenone 21 to the nitro alkene 22 led to the γ-adduct 23 (Org. Chem. Front. 2021, 8, 4758. DOI: 10.1039/D1QO00371B). Xiong-Li Liu of Guizhou University used the Hayashi-Jørgensen amine to mediate the addition of propionaldehyde 25 to the nitroalkene 24, to give an adduct that was added to the enone 26, leading to 27 (Chem. Commun. 2021, 57, 6764. DOI: 10.1039/D1CC02570H).

M. Rita Paleo and F. Javier Sardina of the Universidade de Santiago de Compostela prepared the diester 30 by the addition of the amine 29 to the cyclononadiene 28 (J. Org. Chem. 2021, 86, 13684. DOI: 10.1021/acs.joc.1c01751). Yujiro Hayashi, also of Tohoku University, used the Hayashi-Jørgensen amine to mediate the assembly of 33 by the addition of the diketone 31 to cinnamaldehyde 32 (Org. Lett. 2021, 23, 6654. DOI: 10.1021/acs.orglett.1c02196).

Elizabeth S. Sattely of Stanford University modified Nicotiana benthamiana to synthesize the germination-inhibiting phytoalexin momilactone B (34). From five to seven week old plants, 216 g of leaves yielded 3.6 mg of purified 35. Geranylgeraniol 34 is the biosynthetic precursor to 35, but the plants were raised on just water and fertilizer (Nature Chem. Biol. 2021, 17, 205. DOI: 10.1038/s41589-020-00669-3).

Momilactone B (35), the most active in this series, has not yet been prepared by total synthesis. Pierre Deslongchamps of the Université de Sherbrooke reported the synthesis of the simpler momilactone A (36) (J. Org. Chem. 2002, 67, 5269. DOI: 10.1021/jo025873l).