Other Methods for C-C Ring Construction: Pinolinone (Bach), Agelastatin A (Batey), Panaginsene (Lee), Salvileucalin D, Salvileucalin C (Ding), ent-Codeine (Hudlicky), Walsucochin B (Xie/Shi)
Thorsten Bach of the Technische Universität München used (Chem. Commun. 2014, 50, 3353. ) the chiral medium-mediated photochemical 2+2 cycloaddition that he developed to prepare 3 by combining 1 with 2. Oxidative cleavage led to (-)-Pinolinone (4).
Robert A. Batey of the University of Toronto rearranged (Angew. Chem. Int. Ed. 2013, 52, 10862. ) furfural 5 in the presence of 6 to give the cyclopentenone 7. Acylation followed by intramolecular conjugate addition delivered Agelastatin A (8).
Hee-Yoon Lee of KAIST prepared (Org. Lett. 2014, 16, 2466. ) the tosylhydrazone Na salt 9 from citronellal. Thermolysis led, via a dialkyl diazo intermediate, to the tricyclic 10. Direct comparison of synthetic material with the natural product Panaginsene (11) enabled the assignment of the relative configuration of the pendant methyl group.
Hanfeng Ding of Zhejiang University eliminated (Org. Lett. 2014, 16, 3376. ) HBr from 12 to give, after rearrangement, the cycloheptadiene Salvileucalin D (13). Irradiation converted 13 to the cyclobutene Salvileucalin C (14).
In a recent chapter of his continuing work on the morphine alkaloids, Tomas Hudlicky of Brock University described (Adv. Synth. Catal. 2014, 356, 333. ) the intramolecular [3+2] cycloaddition of the nitrone derived from 15 to give 16. This was readily carried on to ent-Codeine (17).
Xingang Xie and Xuegong She of Lanzhou University used (Org. Lett. 2014, 16, 1996. ) Shi epoxidation and Itsuno-Corey reduction to prepare 18 in enantiomerically-pure form. Cationic cyclization converted 18 to 19, that was oxidized to (-)-Walsucochin B (20).