Thiocarbenium ions cyclization

Cyclization reactions 422.4 Reactions Involving Thiocarbenium Ions... 

Only very rarely have endo-type cyclization reactions triggered by thiocarbenium ions been achieved. One interesting example, involving an aromatic C-nucleophile, is the sulfur analog of the Pictet-Spen-gler reaction, leading to (125), presumably via (124 Scheme 60). Besides the vinyl sulfide (123), the corresponding dithioacetal can also be utilized. 

The development of successful models for stereoselectivity in such cycli-zations is indirect evidence for the intermediacy of an oxocarbenium ion (and iminium ions in the related DDQ-mediated cyclizations of e.g., N-vinyl amides as well as thiocarbenium ions in the analogous sulfur-containing substrates ). Can we go further and resolve whether the mechanism is, in the earlier stages, SET then HAT, or some other combination Essentially we cannot from the published results. It is challenging to interrogate such electron transfer without computational modeling, partly because the electron-transfer events are likely to be much faster than the relatively (glacially) slow movement of molecules and atoms. 

---

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ ]

---