List of used abbreviations - RosDok - Universität Rostock
List of used abbreviations - RosDok - Universität Rostock
List of used abbreviations - RosDok - Universität Rostock
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solution. The use <strong>of</strong> an excess (1.5 equiv.) <strong>of</strong> 4a and <strong>of</strong> TiCl4 also proved to be<br />
important. The formation <strong>of</strong> 5a can be explained by TiCl4-mediated conjugate<br />
addition <strong>of</strong> the terminal carbon atom <strong>of</strong> 3a onto 11a to give intermediate A, cyclization<br />
via the central carbon atom (intermediate B), (Scheme 10), and subsequent<br />
aromatization.<br />
PhS<br />
OSiMe 3<br />
OMe O<br />
3a<br />
OMe<br />
OMe<br />
Me<br />
i<br />
Me<br />
11a 12a (53%)<br />
PhS<br />
TiCl 4<br />
Me 3SiCl<br />
O<br />
O<br />
A<br />
OMe<br />
TiCl 3OMe<br />
Me<br />
TiCl 2(OH)OMe<br />
HCl<br />
29<br />
SPh<br />
SPh O<br />
B<br />
O<br />
OMe<br />
OTiCl2OMe Scheme 10. Possible mechanism <strong>of</strong> the formation <strong>of</strong> 12a; conditions: i: 1) TiCl4,<br />
CH2Cl2, −78 to 20 °C, 20 h; 2) NaHCO3, H2O<br />
Me