Abstract
Chiral pyran derivatives were prepared by hetero-Diels– Alder reaction between ethyl vinyl ether and 1-oxa-1,3-butadienes bearing a chiral substituent in position 4 to obtain more information about the stereoselectivity of this reaction. The structure of reaction products was studied by one-dimensional NMR methods based on a double pulsed field gradient spin echo. Two novel NMR pulse sequences based on a combination of COSY and NOESY/ROESY are described, relieving the problem of heavy overlaps of target resonances in NOE experiments. The NMR studies in combination with further synthetic transformations allowed us to assign the configurations of the isolated cycloadducts. The results indicate that the configuration of the chiral substituent in position 4 is not the principal factor which controls the approach of the ethyl vinyl ether to the planar 1-oxa-1,3-butadiene system. Copyright © 2000 John Wiley & Sons, Ltd.
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