10.1021/jo9609034.s001
Philip Garner
Philip
Garner
Philip B. Cox
Philip B.
Cox
James T. Anderson
James T.
Anderson
John Protasiewicz
John
Protasiewicz
Rebecca Zaniewski
Rebecca
Zaniewski
Use of Silicon-Based Tethers to Control Diastereofacial Selectivity
in Azomethine Ylide Cycloadditions<sup>1</sup>
American Chemical Society
1997
ipolarophile c onjugate
TDC
OCH
Azomethine Ylide Cycloadditions 1
t ether
Control Diastereofacial Selectivity
OSiPh
OCOCH
CH
Azomethine ylides
intramolecular dipolar cycloadditions
OSi
novel approach
diastereofacial selectivity
azomethine ylides
correlation
1997-02-07 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Use_of_Silicon-Based_Tethers_to_Control_Diastereofacial_Selectivity_in_Azomethine_Ylide_Cycloadditions_sup_1_sup_/3703152
A novel approach to controlling the diastereofacial selectivity of
intramolecular dipolar cycloadditions
of azomethine ylides (cf. <b>9</b> → <b>8</b>) by varying the
structure a silicon-based tether is described. A
correlation is found between the length of the <i>t</i>ether
<i>d</i>ipolarophile <i>c</i>onjugate (TDC) and the
observed
sense of diastereocontrol. Azomethine ylides incorporating longer
[OSiPh<sub>2</sub>OCH<sub>2</sub>CH<sub>2</sub>OCOCHCH<sub>2</sub>],
[OSi(i-Pr)<sub>2</sub>OSi(i-Pr)<sub>2</sub>OCH<sub>2</sub>CHCH<sub>2</sub>],
and
[OSiPh<sub>2</sub>OCH<sub>2</sub>CHCH<sub>2</sub>]
TDCs favor endo-si attack (<b>14</b>
→ <b>16</b>, <b>19</b> → <b>20</b>, and <b>21</b>
→ <b>22</b>) while the shorter TDC
[OSiR<sub>2</sub>CH<sub>2</sub>CHCH<sub>2</sub>]
leads to a reversal in
selectivity favoring the endo-re product (<b>23a</b>,<b>b</b>
→ <b>24a</b>,<b>b</b>). Structures of the cycloadducts
have been
assigned on the basis of selected X-ray diffraction data in combination
with chemical/spectral
correlation experiments. The work described herein represents a
conceptually new approach to
stereocontrol and extends the use of silicon-based tethers in
asymmetric synthesis.