Abstract
We have previously clarified that the strongly electron-withdrawing CF3 group nicely affected the base-mediated proton shift of CF3-containing propargylic or allylic alcohols to afford the corresponding α,β-unsaturated or saturated ketones, respectively, which was applied this time to the Claisen rearrangement after O-allylation of the allylic alcohols with a CF3 group, followed by isomerization to the corresponding allyl vinyl ethers via the proton shift, enabling the desired rearrangement in a tandem fashion, or in a stepwise manner, the latter of which was proved to have attained an excellent diastereoselectivity with the aid of a palladium catalyst.
Highlights
It is widely understood that strategic entry of fluorine atoms or fluorinated groups to adequate molecules gave strong impact to the original character in many instances, and the development of novel methods for the construction of a variety of such compounds has attracted significant attention of researchers working in the field of synthetic organic chemistry, material science, and biologically active compounds [1,2,3,4,5]
Its abstraction was realized by the action of such a weak base as diazabicyclo[5.4.0]undec-7-ene (DBU) under the toluene refluxing condition which resulted in the simple isomerization to the intermediates Int-1, followed by the conversion to their keto form 2 to complete this interesting sequence
On the basis of this successful as well as convenient proton shift process starting from the CF3-containing allylic alcohols 1, we envisaged its intriguing extension from the synthetic point of view: our idea was that the bisallylic ethers 3 possibly synthesized in a facile manner by way of the O-allylation of 1 were recognized as the potential substrates for the Claisen rearrangement as long as the proton shift of 3 to 4 was possible
Summary
It is widely understood that strategic entry of fluorine atoms or fluorinated groups to adequate molecules gave strong impact to the original character in many instances, and the development of novel methods for the construction of a variety of such compounds has attracted significant attention of researchers working in the field of synthetic organic chemistry, material science, and biologically active compounds [1,2,3,4,5] For this reason, we have been studying to realize facile preparation of such molecules, and recently reported an interesting proton transfer starting from both propargylic [6] and allylic alcohols [7], enabling to form diverse α,β-unsaturated and saturated ketones, respectively, just by their treatment with very convenient as well as easy-to-handle tertiary amines. We started our research for the novel utilization of the CF3-containing bisallylic ethers 3 as the potent substrates for the Claisen rearrangement via the facile isomerization to the corresponding allyl vinyl ethers 4
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