Reagents, unstable, reactions Isomerization

In 1912 Oddo reported the results of an investigation of the products obtained on carbonation of both the 2- and 3-methylindole Grignard reagents. In the former case the relatively unstable l-carboxy-2-methylindole (377) was the main product obtained when the reaction was carried out at temperatures up to 35° however, at 110° the isomeric 3-carboxy-2-methylindole (378) was the major product formed. According to Oddo l-carboxy-3-methylindole (379) is more stable than the corresponding 2-methyl compound (i.e., 377) and can be obtained by carbonation of the skatole Grignard reagent at 100°. ... 

Occasionally, alkenes suffer migrations80 or cis-trans isomerizations6d during Dess-Martin oxidations. Such reactions normally only occur under very favourable thermodynamic and kinetic conditions, Dess-Martin reagent being able to deliver compounds containing unstable alkenes that would isomerize on simple contact with silica. 

The same group also applied boron reagents to trap reactive dienes and used them in a subsequent IMDA reaction [20b]. o-Quinodimethanes are useful dienes since they allow rapid access to the tetralin skeleton. However, they are fairly unstable and only undergo cycloaddition with reactive dienophiles in the presence of less reactive dienophiles, the diene isomerizes or dimerizes preferentially. 

Flash chemistry makes highly short-lived reactive species usable as starting materials or reagents for chemical synthesis. In short, unstable reactive species can be generated and transferred to another location to be used in the next reaction before they decompose or isomerize based on high-resolution reaction time control. Therefore, chemical reactions that are practically impossible in batch macroreactors should be made possible by flash chemistiy. 

---