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5-Hydroxyalkyl derivatives of <i>tert</i>-butyl 2-oxo-2,5-dihydro-1<i>H</i>-pyrrole-1-carboxylate: diastereoselectivity of the Mukaiyama crossed-aldol-type reaction
Auteur(s)
Vallat, Oliver
Buciumas, Ana-Maria
Date de parution
2009
In
Acta Crystallographica Section C : Crystal Structure Communications, International Union of Crystallography, 2009/C65/4/o171-o175
Résumé
The title compounds, <i>rac</i>-(1'<i>R</i>,2<i>R</i>)-<i>tert</i>-butyl 2-(1'-hydroxyethyl)-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1<i>H</i>-pyrrole-1-carboxylate, C<sub>17</sub>H<sub>2</sub>0N<sub>2</sub>O<sub>6</sub>, (I), <i>rac</i>-(1'<i>S</i>,2<i>R</i>)- <i>tert</i>-butyl 2-[1'-hydroxy-3'-(methoxycarbonyl)propyl]-3-(2-nitrophenyl)-5-oxo-2,5-dihydro-1<i>H</i>-pyrrole-1-carboxylate, C<sub>20</sub>H<sub>24</sub>N<sub>2</sub>O<sub>8</sub>, (II), and <i>rac</i>-(1'<i>S</i>,2<i>R</i>)- <i>tert</i>-butyl 2-(4'-bromo-1'-hydroxybutyl)-5-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate, C<sub>13</sub>H<sub>20</sub>BrNO<sub>4</sub>, (III), are 5-hydroxyalkyl derivatives of <i>tert</i>-butyl 2-oxo-2,5-dihydropyrrole-1-carboxylate. In all three compounds, the <i>tert</i>-butoxycarbonyl (Boc) unit is orientated in the same manner with respect to the mean plane through the 2-oxo-2,5-dihydro-1<i>H</i>-pyrrole ring. The hydroxyl substituent at one of the newly created chiral centres, which have relative <i>R,R</i> stereochemistry, is <i>trans</i> with respect to the oxo group of the pyrrole ring in (I), synthesized using acetaldehyde. When a larger aldehyde was used, as in compounds (II) and (III), the hydroxyl substituent was found to be <i>cis</i> with respect to the oxo group of the pyrrole ring. Here, the relative stereochemistry of the newly created chiral centres is <i>R,S</i>. In compound (I), O-H···O hydrogen bonding leads to an interesting hexagonal arrangement of symmetry-related molecules. In (II) and (III), the hydroxyl groups are involved in bifurcated O-H···O hydrogen bonds, and centrosymmetric hydrogen-bonded dimers are formed. The Mukaiyama crossed-aldol-type reaction was successful when using the 2-nitrophenyl-substituted hydroxypyrrole, or the unsubstituted hydroxypyrrole, and boron trifluoride diethyl ether as catalyst. The synthetic procedure leads to a <i>syn</i> configuration of the two newly created chiral centres in all three compounds.
Identifiants
Type de publication
journal article
