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37.1.4.1.3 Variation 3: Substitution of Pent-4-enyl Ethers

DOI: 10.1055/sos-SD-037-00115

McDonald, F. E.Science of Synthesis, (200837136.

Benzylic pent-4-enyl ethers 18 undergo cyclization with transetherification in the presence of iodine to provide iodotetrahydrofuran diastereomers cis- and trans-19 (Scheme 6).[‌11‌] The cyclizationtransetherification proceeds with particularly high 2,5-stereoselectivity for cis-19 starting from 2,6-dichlorobenzyl ether (18, R1=Cl), and yields and stereoselectivities are generally higher than the corresponding iodocyclizations of pent-4-en-1-ols or silyl ethers. Analogous transetherifications have also been accomplished starting with the tert-butyl ether 20.[‌12‌] These findings have been extended to structurally complex substrate 22 and its diastereomer 23,[‌13‌] which demonstrates that the stereoselectivity of transetherificationcyclization is dependent upon stereoinduction from an allylic alcohol substituent, rather than the configuration of the benzyl ether.

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References