1) "Bulb-to-bulb" distillation is a simple method to separate volatile product from non-volatile by-products, with near-to-zero possibilities to separate two (or more ) volatile products. This procedure you can replace by molecular distillation - simply use sublimation appparatus for some drop quantities or cold-finger with CO2/LN2 cooling for greater ones.

2) Send here DOI of original publication - I'll try to analyze what reason of use such rare triflating conditions/reagents. In common case, triflic anhydride +MeIm (DBU) works well.

Maybe isomerisation of the double bond happens with excess phntf2

Halder

I agree with Wintner th at you would get isomeric mixture. See

--- Forbus, T. R., Jr. et al. Journal of Organic Chemistry, 52(19), 4156-9; 1987

You should also perform your reaction at very low temp. -78 !

see

--- Augeri, David J. et al. U.S. Pat. Appl. Publ., 20020055631, 09 May 2002

" A -78°C. solution of cyclohexanone (1.54 g, 10 mmol) and N-phenyl(trifluoromethanesulfonamide) (3.75 g, 10.5 mmol) in THF (20 mmol) was treated with 1M NaHMDS in THF (11 mL), warmed to room temperature, filtered through a pad of silica gel (10 g) with diethyl ether (5 mL), and concentrated. The concentrate was purified by flash column chromatography on silica gel with 1% ethyl acetate/hexanes. "

Good luck

https://pubs.acs.org/doi/pdf/10.1021/ja00350a044?download=true

Hi, Thank you all for the responses.

Dear Mr Rogoza,

So I am preparing 2-methylcyclohex-1-en-1-yl trifluoromethanesulfonate, according to the procedures in

1. https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.201203646

See Supp Info

2. https://pubs.acs.org/doi/abs/10.1021/ja00336a033

Should I expect my molecule to be UV active?

Thanks

Dear Mr Wintner and Mr Amer, thanks for the answers.

PhNTf2 appears to be the standard reagent for the generation of the thermodynamic enol triflate, as can be seen from the attached Refs

1. https://pubs.acs.org/doi/abs/10.1021/ja00336a033

2. https://pubs.acs.org/doi/pdf/10.1021/ar00146a001

So the major ones should by the desired thermodynamic ones.

1) Should I expect my molecule to be UV active? - definitely YES. Unsaturated C=C bond, additionally conjugated with -O- .

2) I have checked original publication cited by you, it refer to

McMurry, J. E.; Scott, W. J. Tetrahedron Lett. 1983, 24, 979-982 (original method of triflating with PhNTf2) . The reason of development was follow:

"Triflic anhydride, the most often-used triflating reagent, gives only poor to moderate yields of products on reaction with enolates in tetrahydrofuran."

No wonder!!! - THF and Tf2O reacts rapidly to TfO-CH2CH2CH2CH2-OTf !! :-)

I am sure that Tf2O + MeIm/DBU/collidine will work perfectly in hexane. The last method is very convenient as collidine triflate is not soluble in hexane Tetrahedron: Asymmetry, V.8., N.6., pp.957-963(1997) .

3) Method used by you is relative simple so I recommend to test reagents and solvents quality. To collect some ml of product, you can use molecular distillation (temperature below 10-15oC of boiling temperature at given vacuum level); as simple fraction collector you can use hand-made cone from aluminium foil same to ALDRICH glassware https://www.sigmaaldrich.com/catalog/product/aldrich/z129607?lang=en®ion=RU&cm_sp=Insite-_-prodRecCold_xviews-_-prodRecCold10-1 - place it in bottom and finaly collect distillate with pipette - it replace bulb-to-bulb equipment for minute amounts.

Thanks Mr Rogoza for the helpful info. I agree that the procedure I am using is supposed to be relatively simple, and I was worried because I repeated it twice with no results.

I guess I will have a more careful look at the reagents and solvents then.

I will update here if something useful comes up.

Thnaks

Thank you all of you for your valuable suggestions.

I just wanted to make a few updates for this problem.

I finally managed to get my product with more careful procedure.

The reaction seems extremely sensitive to moisture. Even the slightest amount of moisture causes many more extra UV active spots to appear, most of which were KMnO4 active also. The extra KMnO4 active spots arise probably from the by product PhNHTf (and other amine containing byproducts), since KMnO4 can oxidise the amine.

Moreover, the desired product Triflate is not UV active at all due to the strong electron withdrawing OTf group attached to it. Also, due to the same reason, it gives KMnO4 spot only on heating the TLC plate for longer times; on the other hand, the PhNHTf spots, as well as other spots appear on the KMnO4 readily, with slight heating.

It is also particularly nonpolar, with an Rf of about .35 in Hexane solvent, and .85 in 1:5 (EtOAc/Hex). I was confused about the Rf since I assumed that the presence of SO2CF3 group will make it more polar.

Dear Saayak, look at "PREPARATION OF VINYL TRIFLUOROMETHANE-SULFONATES: 3-METHYL-2-BUTEN-2-YL TRIFLATE" :

http://orgsyn.org/demo.aspx?prep=cv6p0757

3-methyl-2-buten-2-yl triflate : end absorption in the UV (heptane, ε 700 at 210 nm)

Procedure use also simple (less exotic) Tf2O +Py - as it was recommended in my previous note.

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