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Stepwise Preparation of All-Cis 1,3,4-trifluoro-2-phenylcyclohexane, Avoiding a Phenonium Intermediate

Stepwise Preparation of All-Cis 1,3,4-trifluoro-2-phenylcyclohexane, Avoiding a Phenonium Intermediate

Alastair J Durie, Tomoya Fujiwara, Nawaf Al-Maharik, Alexandra M Z Slawin, David O'Hagan

J Org Chem. 2014 Sep 5;79(17):8228-33.

PMID: 25102142

Abstract:

The original synthesis of all-cis 1,2,4,5,-tetrafluoro-2-phenylcyclohexane resulted in a trifluorocyclohexene as a significant co-product of the final fluorination step. This product was notable in that an elimination reaction was accompanied by C-F bond formation that had occurred with a retention of configuration. In order to deconvolute this reaction, the two isomers of the ditriflate diol precursor were separated, and they were each treated independently with Et3N·3HF. One gave the original all-cis 1,2,4,5,-tetrafluoro-2-phenylcyclohexane and the other the trifluorocyclohexene. A deuterium labeling experiment was carried out, resulting in a distribution of the isotope in the trifluorocyclohexene consistent with an intermediate (symmetrical) phenonium intermediate. Cognisant of this, a controlled elimination reaction of one of the diastereoisomers with DBU, followed by hydrogenation, gave a cyclohexane triflate, which, on fluorination, gave the all-cis 1,2,3-trifluoro-2-phenylcyclohexane now with an inversion of configuration.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP827521	Phenylcyclohexane		827-52-1	Price

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