+
8
2.2,ꢀ81.2,ꢀ70.9,ꢀ70.0,ꢀ56.0,ꢀ55.9,ꢀ55.7ꢀ(2ꢀC),ꢀ24.0,ꢀ23.8,ꢀ22.6,ꢀ22.4;ꢀHRMSꢀ(ES)ꢀcalcdꢀforꢀ[C15
20 4
H O ꢀ+ꢀNa] ꢀ
calcdꢀ287.1254,ꢀfoundꢀ287.1272.ꢀꢀ
ꢀ
2
-Isopropoxy-5-(thiophen-2-yl)-2,5-dihydrofuranꢀ (26):ꢀ Thisꢀ reactionꢀ wasꢀ performedꢀ accordingꢀ toꢀ theꢀ
generalꢀprocedureꢀforꢀ2,5-dihydrofuransꢀusingꢀ(Z)-4-isopropoxy-1-(thiophen-2-yl)but-3-en-1-olꢀ(0.212ꢀg,ꢀ
1
3
.00ꢀmmol),ꢀandꢀstirringꢀforꢀ1.5ꢀh.ꢀꢀTheꢀcrudeꢀproductꢀwasꢀpurifiedꢀbyꢀcolumnꢀchromatographyꢀ(silicaꢀgel,ꢀ
%ꢀEtOAc/hexanes)ꢀtoꢀgiveꢀ91%ꢀofꢀtheꢀproductꢀ(191ꢀmg,ꢀ0.907ꢀmmol)ꢀasꢀaꢀpaleꢀyellowꢀoil.ꢀꢀTheꢀproductꢀ
wasꢀisolatedꢀasꢀaꢀ1:1ꢀmixtureꢀofꢀdiastereomers.ꢀꢀFTIRꢀ(film,ꢀcm-1):ꢀ3087,ꢀ2971,ꢀ2891,ꢀ2244,ꢀ1624,ꢀ1465,ꢀ
1
1
=
1
1
2
438,ꢀ1378,ꢀ1343,ꢀ1310;ꢀ HꢀNMRꢀ(CDCl
3
,ꢀ400ꢀMHz):ꢀδꢀ7.24ꢀ(m,ꢀ1H),ꢀ7.00ꢀ(m,ꢀ1H),ꢀ6.93ꢀ(m,ꢀ1H),ꢀ6.21ꢀ(dt,ꢀJꢀ
ꢀ5.9,ꢀ1.2ꢀHz,ꢀ0.5H),ꢀ6.18ꢀ(m,ꢀ0.5H),ꢀ6.12(m,ꢀ0.5H),ꢀ6.07ꢀ(m,ꢀ0.5H),ꢀ5.93ꢀ(m,ꢀ1H),ꢀ5.89(m,ꢀ1H),ꢀ4.00ꢀ(m,ꢀ
1
3
3
H),ꢀ1.26ꢀ(d,ꢀJꢀ=ꢀ6.2ꢀHz,ꢀ1.5H),ꢀ1.20ꢀ(m,ꢀ4.5H);ꢀ CꢀNMRꢀ(CDCl ,ꢀ100ꢀMHz):ꢀδꢀ145.0,ꢀ144.1,ꢀ134.8,ꢀ134.3,ꢀ
27.8,ꢀ127.2,ꢀ126.8,ꢀ126.5,ꢀ125.9,ꢀ125.7,ꢀ125.3,ꢀ125.1,ꢀ107.1,ꢀ106.7,ꢀ82.1,ꢀ81.7,ꢀ70.5,ꢀ70.2,ꢀ23.8,ꢀ23.7,ꢀ
+
2.4,ꢀ22.1;ꢀHRMSꢀ(ES)ꢀcalcdꢀforꢀ[C11
H
14
O
2
Sꢀ+ꢀNa] ꢀcalcdꢀ233.0607,ꢀfoundꢀ233.0605.ꢀ
ꢀ
-Isopropoxy-6,6,8,8-tetramethyl-1,7-dioxaspiro[4.4]non-3-eneꢀ (27a):ꢀ Thisꢀ reactionꢀ wasꢀ performedꢀ
2
accordingꢀ toꢀ theꢀ generalꢀ procedureꢀ forꢀ 2,5-dihydrofuransꢀ usingꢀ (Z)-3-(3-isopropoxallyl)-2,2,5,5-
tetramethyltetrahydrofuran-3-olꢀ (0.242ꢀ g,ꢀ 1.00ꢀ mmol),ꢀ andꢀ stirringꢀ forꢀ 17ꢀ h.ꢀ ꢀ Theꢀ crudeꢀ productꢀ wasꢀ
purifiedꢀbyꢀcolumnꢀchromatographyꢀ(silicaꢀgel,ꢀ4%ꢀEtOAc/hexanes)ꢀtoꢀgiveꢀ77%ꢀofꢀtheꢀproductꢀ(185ꢀmg,ꢀ
0
.770ꢀ mmol)ꢀ asꢀ aꢀ colorlessꢀ oil.ꢀ ꢀ Theꢀ productꢀ wasꢀ isolatedꢀ asꢀ aꢀ 3:1ꢀ mixtureꢀ ofꢀ diastereomers,ꢀ theꢀ
assignmentꢀ ofꢀ diastereomersꢀ wasꢀ notꢀ clearꢀ fromꢀ NOESYꢀ experiment.ꢀ ꢀ FTIRꢀ (film,ꢀ cm-1):ꢀ 2971,ꢀ 2931,ꢀ
1
1
465,ꢀ1378,ꢀ1066,ꢀ1025,ꢀ1006,ꢀ742;ꢀ HꢀNMRꢀ(CDCl
3
,ꢀ400ꢀMHz):ꢀδꢀ6.03-6.00ꢀ(m,ꢀ1H),ꢀ5.86ꢀ(m,ꢀ1H),ꢀ5.84ꢀ
(
dd,ꢀJꢀ=ꢀ6.0,ꢀ1.0ꢀHz,ꢀ0.35H),ꢀ5.77ꢀ(dd,ꢀJꢀ=ꢀ5.9,ꢀ1.2ꢀHz,ꢀ0.65H),ꢀ4.07-3.95ꢀ(m,ꢀ1H),ꢀ2.33ꢀ(d,ꢀJꢀ=ꢀ13.4ꢀHz,ꢀ
0
1
.35H),ꢀ2.23ꢀ(d,ꢀJꢀ=ꢀ13.3ꢀHz,ꢀ0.65H),ꢀ2.03ꢀ(d,ꢀJꢀ=ꢀ13.4ꢀHz,ꢀ0.35H),ꢀ1.93ꢀ(d,ꢀJꢀ=ꢀ13.3ꢀHz,ꢀ0.65H),ꢀ1.38ꢀ(m,ꢀ3H),ꢀ
.32ꢀ(m,ꢀ3H),ꢀ1.31ꢀ(m,ꢀ2H),ꢀ1.25ꢀ(m,ꢀ1.65H),ꢀ1.24ꢀ(m,ꢀ3.35H),ꢀ1.20ꢀꢀ(m,ꢀ1.35H),ꢀ1.18-1.17ꢀ(m,ꢀ4.65H),ꢀ1.13ꢀ
1
3
(
m,ꢀ1H);ꢀ CꢀNMRꢀ(CDCl
3
,ꢀ100ꢀMHz):ꢀδꢀ134.3,ꢀ134.0,ꢀ128.2,ꢀ127.5,ꢀ106.7,ꢀ105.9,ꢀ100.4,ꢀ100.2,ꢀ85.3,ꢀ85.0,ꢀ
7
9.2,ꢀ78.6,ꢀ70.3,ꢀ70.1,ꢀ50.2,ꢀ49.9,ꢀ31.4,ꢀ31.3,ꢀ30.3,ꢀ29.9,ꢀ28.0,ꢀ27.6,ꢀ24.5,ꢀ23.8,ꢀ23.5,ꢀ22.9,ꢀ22.5,ꢀ21.9;ꢀ
+
HRMSꢀ(ES)ꢀcalcdꢀforꢀ[C14
24 3
H O ꢀ+ꢀNa] ꢀcalcdꢀ263.1618,ꢀfoundꢀ263.1609.ꢀꢀ
References:ꢀ
1
2
3
4
. Yamamoto,ꢀY.;ꢀYatagai,ꢀH.;ꢀSaito,ꢀY.;ꢀMaruyama,ꢀK.ꢀJ.ꢀOrg.ꢀChem.ꢀ1984,ꢀ49,ꢀ1096.ꢀ
. Tzeng,ꢀD.;ꢀWeber,ꢀW.ꢀP.ꢀJ.ꢀOrg.ꢀChem.ꢀ1981,ꢀ46,ꢀ265.ꢀ
. Jenner,ꢀG.ꢀTetrahedronꢀLett.ꢀ1988,ꢀ29,ꢀ2445.ꢀ
. Chen,ꢀW.;ꢀYang,ꢀX.ꢀD.;ꢀLi,ꢀY.;ꢀYang,ꢀL.ꢀJ.;ꢀWang,ꢀX.ꢀQ.;ꢀZhang,ꢀG.ꢀL.;ꢀZhang,ꢀH.ꢀB.ꢀOrg.ꢀBiomol.ꢀChem.ꢀ
2
011,ꢀ9,ꢀ4250.ꢀ
5
. Mangold,ꢀS.ꢀL.;ꢀCarpenter,ꢀR.ꢀT.;ꢀKiessling,ꢀL.ꢀL.ꢀOrg.ꢀLett.ꢀ2008,ꢀ10,ꢀ2997.ꢀ
S19ꢀ
ꢀ