TY - JOUR
T1 - Cycloadditions, 55
T2 - Substituent effects in tandem intramolecular silyl nitronate olefin cycloadditions (ISOC) leading to functionalized tetrahydrofurans
AU - Hassner, Alfred
AU - Friedman, Oded
AU - Dehaen, Wim
PY - 1997/3
Y1 - 1997/3
N2 - The intramolecular silyl nitronate olefin cycloaddition (ISOC) leading to substitued, fused-ring tetrahydrofurans 6 was examined with regard to optimum conditions and substituent effects. The required unsaturated nitro ethers 3 resulted from low-temperature, base-mediated Michael addition of allyl alcohols 2 to nitroolefins 1, followed by conversion to unsaturated silyl nitronates 4. Cycloaddition of the latter and elimination of silanol provided 6. One-pot tandem reactions, starting with nitroolefins 1 and allyl alcohols 2 and involving four steps, sometimes proceeded in better yields but often gave unexpected side products. Terminal olefinic electron-donating substituents (Me, MeO) increased the rate of cycloaddition, while an internal olefinic methyl substituent slowed down the reaction. In the case of nitronates possessing ester or nitrile moieties as terminal olefin substituents, tandem Michael addition to produce substituted furans 14, 15 occurred faster than trapping of the nitronate anion by TMSCl.
AB - The intramolecular silyl nitronate olefin cycloaddition (ISOC) leading to substitued, fused-ring tetrahydrofurans 6 was examined with regard to optimum conditions and substituent effects. The required unsaturated nitro ethers 3 resulted from low-temperature, base-mediated Michael addition of allyl alcohols 2 to nitroolefins 1, followed by conversion to unsaturated silyl nitronates 4. Cycloaddition of the latter and elimination of silanol provided 6. One-pot tandem reactions, starting with nitroolefins 1 and allyl alcohols 2 and involving four steps, sometimes proceeded in better yields but often gave unexpected side products. Terminal olefinic electron-donating substituents (Me, MeO) increased the rate of cycloaddition, while an internal olefinic methyl substituent slowed down the reaction. In the case of nitronates possessing ester or nitrile moieties as terminal olefin substituents, tandem Michael addition to produce substituted furans 14, 15 occurred faster than trapping of the nitronate anion by TMSCl.
KW - Dipolar cycloadditions
KW - Isoxazolidines
KW - Silyl nitronates
KW - Tandem Michael additions
KW - Tetrahydrofurans
UR - http://www.scopus.com/inward/record.url?scp=33748825216&partnerID=8YFLogxK
U2 - 10.1002/jlac.199719970321
DO - 10.1002/jlac.199719970321
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AN - SCOPUS:33748825216
SN - 0947-3440
SP - 587
EP - 594
JO - Liebigs Annales
JF - Liebigs Annales
IS - 3
ER -