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New mechanism for internal nucleophilic substitution reactions.


A new mechanism of the classic internal nucleophilic substitution reactions SNi by means of computational studies in gas-phase, DCM and acetonitrile is reported. Despite the importance of the SNi mechanism, since the mid-1990s this mechanism has remained unexplored. The study has focused mainly on the comparison between the mechanisms postulated to date for the SNi reactions and a new mechanism suggested by us that fits better the experimental observations. The comparative study has been applied to the conversion of ethyl, neopentyl, isopropyl and tert-butyl chlorosulfites into the corresponding alkyl chlorides. This new mechanism occurs through two transition structures. For primary and secondary substrates, the first transition structure is a 6-center syn-rearrangement of the alkanesulfonyl chloride that produces the corresponding olefin by simultaneous expulsion of HCl and SO2. The olefin, HCl and SO2 form a molecular complex. The final syn addition of HCl to the olefin leads to the alkyl chloride with retention of configuration. For tertiary substrates a variation of the previous mechanism is postulated with the intervention of contact ionic pairs. It is of great importance to emphasize that the new mechanism is able to explain some experimental observations such as the presence of olefins in this type of reactions and the low reactivity of some systems such as neopentyl chlorosulfite. Our results pave the way to a new mechanistic perspective in similar reactions which will need further studies and validation.

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Publication details

The article was received on 04 Dec 2017, accepted on 12 Jan 2018 and first published on 12 Jan 2018

Article type: Paper
DOI: 10.1039/C7OB02994B
Citation: Org. Biomol. Chem., 2018, Accepted Manuscript
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    New mechanism for internal nucleophilic substitution reactions.

    R. J. Zaragoza, M. J. Aurell and M. A. González-Cardenete, Org. Biomol. Chem., 2018, Accepted Manuscript , DOI: 10.1039/C7OB02994B

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