Organocatalyzed Ring Construction: The Lin/Wei Synthesis of δ-Lycorane
Marta Meazza and Ramon Rios of the University of Southampton and Jan Vesely of Charles University achieved (Eur. J. Org. Chem. 2017, 1749. ) high enantioselectivity in the preparation of 2 by the addition of 1 to crotonaldehyde. Akkattu T. Biju, now at the Indian Institute of Science Bangalore, showed (ACS Catal. 2017, 7, 3995. ) that the cyclization of 3 to 4 could also proceed in high ee. Xing-Wang Wang of Soochow University reported (Adv. Synth. Catal. 2017, 359, 1541. ) related results.
Jinxing Ye of the East China University of Science and Technology assembled (Org. Lett. 2017, 19, 2322. ) 7 by adding the photoenol from 6 in a conjugate sense to 5. Ying-Chun Chen of Sichuan University added (Chem. Eur. J. 2017, 23, 2945. ) the cross-conjugated dienone 8 to 9, leading to 10. Masahisa Nakada of Waseda University cyclized (Org. Lett. 2017, 19, 2390. ) the nitro aldehyde 11 to 12. Fangzhi Peng and Zhihui Shao of Yunnan University combined (Adv. Synth. Catal. 2017, 359, 89. ) 13 and 14 to give an intermediate that they carried on, via selective hydration of the alkyne to a ketone, to the cyclohexanone 15. Professor Chen and Qin Ouyang of the Third Medical Military University combined (Nature Chem. 2017, 9, 590. ) 16 with 17 to give 18. Ramesh C. Samanta and Hisashi Yamamoto of Chubu University devised (J. Am. Chem. Soc. 2017, 139, 1460. ) an organocatalyst that mediated the brominative cyclization of 19 with 20, leading to 21.
Strategies have been developed for the assembly of other polycyclic products. In a two-step, one-pot process, Peng-Fei Xu of Lanzhou University added (Org. Lett. 2017, 19, 2130. ) 22 to 23 in high de and ee, then cyclized that product with a Stetter-type catalyst to give 24. Miquel A. Pericas of ICIQ developed (ACS Catal. 2017, 7, 1383. ) a robust immobilized version of the Luo catalyst that could be used in flow. In practice, the addition of 25 to 26 was carried out in batch mode, then the resulting solution was flowed through the immobilized catalyst. Using 0.7 mmol of catalyst, 11.7 g of 27 was prepared in one 24-h operation.
While not a natural product itself, δ-lycorane (31) is the parent ring system of many of the Amaryllidaceae alkaloids. Jun Lin and Kun Wei of Yunnan University established (Org. Chem. Front. 2017, 4, 1149. ) the relative and absolute configuration of 31 by adding the β-keto ester 28 to the nitro alkene 29 to give 30.