1,2-Halogen Migration in Haloallenyl Ketones:  Regiodivergent Synthesis of Halofurans

Abstract

Selective 1,2-iodine, bromine, and chlorine migration in haloallenyl ketones in the presence of Au catalyst has been demonstrated. It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively. Halirenium intermediate was proposed for the unusual 1,2-halogen migration. This cascade transformation allows for mild and efficient synthesis of various types of 3-halofurans.

Two-fold tandem acyl-group shift/cyclization via gold catalysis

“…Activation of the terminal allenic position by gold in 9-Au allows its activation and the furan ring of 6 eventually forms via 5-endo-dig cyclization presumably through equilibrium 10 (Cycle III in Scheme 4). [32][33] A similar reactivity of allenones has been recently reported by Alcaide and Almendros for the synthesis of 2-substituted furans via Au(I) catalysis. 34 Propargylic allenols The overall selectivity of this cascade is indeed outstanding reasoning on the sequential order of molecular events that readily takes place.…”

Metal‐Catalyzed [1,2]‐Alkyl Shift in Allenyl Ketones: Synthesis of Multisubstituted Furans

“…Thus, the migratory aptitude of a phenyl vs. that of a methyl group (> 100:1) is in good agreement with that reported in the literature for rearrangements of cations. [17] Although a mechanism involving [1,2]-alkyl shift in the carbenoid intermediate 12 [5,8] (Scheme 1, path C) cannot be completely ruled out at this point, it is considered to be less likely. [18,19] In summary, we have developed a novel metal-catalyzed method for the synthesis of furans, which proceeds by an unprecedented [1,2]-alkyl shift in allenyl ketones.…”

Metal-mediated synthesis of furans and pyrroles

“…8 For this reaction iodo and bromo allenyl ketones gave best results, compared to their chloro analogue. This chemistry is interesting not only as a novel cascade transformation but also serves as a mild, selective, and efficient approach to different types of 3-halofurans 10.…”