stereoisomer. Interestingly, ketones rather than vinyl triflates were isolated when
Et 2 O was used as the solvent instead of CH 2 Cl 2 .
Ph
TBSO
SiMe 2 Ph
BnOCH 2 CHO 109
109
SnCl 4 , CH 2 Cl 2 , -55 °C
85%
O
PhMe 2 Si
OBn
Ph
OTBS
O
PhMe 2 Si
OBn
Ph
OTBS
BnOCH 2 CHO
BF 3 •Et 2 O, CH 2 Cl 2 , -78 °C
78%
Ph
CHO
1) PhMe 2 Si
B
O
O
CO 2 i-Pr
CO 2 i-Pr
2) TBSCl, Et 3 N, DMAP
ClCH 2 CH 2 Cl, reflux
-78 °C, 4 Å MS
81%
106
107
108
(dr >20:1)
110
111 (dr = 2-:1)
Scheme 30 Use of [3+2]-cycloadditions to tetrahydrofurans by Roush and Micalizio [31]
H
H
H
BnO
O
R
SiMe 2 Ph
BF 3
major
H
H
H
O
R
SiMe 2 Ph
F 3 B
OBn
minor
O
PhMe 2 Si
R
OBn
O
PhMe 2 Si
R
OBn
2,5-syn-113
2,5-anti-116
H
BnO
O
H
H
H
O
R
SiMe 2 Ph
OBn
SnCl 4
H
H
R
SiMe 2 Ph
Cl 4 Sn
major
minor
112
115
117
114
Scheme 31 Mechanistic hypothesis for cis- and trans-tetrahydrofuran formation by Roush and
Micalizio [31]
14
J.D. Rainier