Cationic cyclization reactions with alkyne terminating groups: a useful tool in biomimetic synthesis

Cyclization reactions through cationic intermediates have become a highly valuable tool in organic synthesis. The use of alkynes as the terminating group in this type of cationic processes offers wide...

Aza-heterocyclic frameworks through intramolecular π-system trapping of spiro-N-acyliminiums generated from isoindolinone

Spiro-acetoxylactams, obtained easily by the tandem carbonyl reduction/O-acylation, were submitted to acids giving through π-cationic cyclization aza-heterocyclic systems including amino-acids.

The intramolecular reaction of acetophenone N-tosylhydrazone and vinyl: Brønsted acid-promoted cationic cyclization toward polysubstituted indenes

In the presence of TsNHNH2, a Brønsted acid-promoted intramolecular cyclization of o-(1-arylvinyl) acetophenone derivatives was developed, leading to polysubstituted indenes with complexity and diversity in moderate to excellent yields.

Construction of a diverse set of terpenoid decalin subunits from a common enantiomerically pure scaffold obtained by a biomimetic cationic cyclization

An unprecedented biomimetic cationic cyclization reaction is used for the synthesis of an enantiomerically pure scaffold that is easily transformed into a set of structurally diverse decalin derivatives with potential application in the synthesis of targeted natural products and/or natural-product-inspired new molecules.

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 enone 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.