# Is (2R,3S)-3,4-dimethylpentan-2-ol feasible to be dehydrated with POCl3 and pyridine?

I was given a problem of reaction between (2R,3S)-3,4-dimethylpentan-2-ol and $$\ce{POCl3}$$ and pyridine. I know that $$\ce{POCl3}$$ will be attacked with hydroxyl group and the hydrogen on hydroxyl will be cleaved with pyridine so the hydroxyl group becomes good leaving group.

The reaction mechanism proceeds on E2 mechanism no matter whether the alcohol is primary, secondary, or tertiary. The problem is E2 mechanism can proceed if the stereochemistry of antiperiplanarity is fulfilled. When I drawn the stereochemistry of the alcohol, it turned that methyl on alpha-carbon and beta-carbon made the beta-hydrogen on these carbons cis to the hydroxyl group (the methyl on alpha carbon is wedge so the bonded hydrogen and hydroxyl group are dash), thus the reaction can not proceed.

Is that correct? If it is correct, will the reaction mechanism proceed on other mechanism?

The reaction will take place via E2 mechanism as the C2-C3 $$\sigma$$ bond will undergo rotation, giving the product. The concentration of the minor product will also be comparatively more as compared to the (2R,3R) or (2S,3S) form, but it will not form the major product. Stereochemistry plays an important role in these reactions when the C-C bond cannot rotate about it's axis and hence no reaction occurs. An example is given below: