The synthetic use of 2-alkyl and 2-(hetero)aryl substituted (Z)- and (E)-1-trimethylsilyl-1-trimethylstannylethenes of general formula (Z)-2, (E)-2, (Z)-3 and (E)-3, via the corresponding 1-silylethenyllithiums prepared by tin-lithium exchange reactions and via Lewis acid- or palladium-mediated carbon-carbon bond forming reactions has been investigated. The 1-silylethenyllithiums prepared either from (Z)-2 and (Z)-3 or from (E)-3 have been found to be useful intermediates for the synthesis of 1,2-disubstituted (E)-ethenyltrimethylsilanes such as (E)-6, (E)-7, (E)-13a, (E)-13b, (E)-13d, (E)-13e and (E)-13f. Moreover, the (E)-1-silylethenyllithium derived from (Z)-3c (R = 2-thienyl) can rearrange at -78-degrees-C to give (E)-2-(5-lithium-2-thienyl)ethenyltrimethylsilane, (E)-24. This rearrangement provides a stereospecific route for the preparation of (E)-2-trimethylsilylethenylthiophenes substituted in the 5-position by an alkyl or a functional group. Either the Lewis acid- or the palladium-mediated reactions between acyl halides and (Z)-2 or (E)-2 are chemoselective but non-stereospecific. On the contrary, the palladium-mediated reaction between (Z)-3a (R = phenyl) and benzoyl chloride is stereospecific and affords the 1-sily ketone (E)-38 in a high yield. Finally, the configuration of the 1,2-disubstituted ethenyltrimethylsilanes synthesized during these studies has been unambiguously assigned by NMR spectroscopy.
STUDIES ON THE SYNTHETIC USE OF STEREODEFINED OLEFINS WITH GEMINAL TRIMETHYLSILYL AND TRIMETHYLSTANNYL SUBSTITUENTS
ROSSI, RENZO;CARPITA, ADRIANO;BELLINA, FABIO;
1991-01-01
Abstract
The synthetic use of 2-alkyl and 2-(hetero)aryl substituted (Z)- and (E)-1-trimethylsilyl-1-trimethylstannylethenes of general formula (Z)-2, (E)-2, (Z)-3 and (E)-3, via the corresponding 1-silylethenyllithiums prepared by tin-lithium exchange reactions and via Lewis acid- or palladium-mediated carbon-carbon bond forming reactions has been investigated. The 1-silylethenyllithiums prepared either from (Z)-2 and (Z)-3 or from (E)-3 have been found to be useful intermediates for the synthesis of 1,2-disubstituted (E)-ethenyltrimethylsilanes such as (E)-6, (E)-7, (E)-13a, (E)-13b, (E)-13d, (E)-13e and (E)-13f. Moreover, the (E)-1-silylethenyllithium derived from (Z)-3c (R = 2-thienyl) can rearrange at -78-degrees-C to give (E)-2-(5-lithium-2-thienyl)ethenyltrimethylsilane, (E)-24. This rearrangement provides a stereospecific route for the preparation of (E)-2-trimethylsilylethenylthiophenes substituted in the 5-position by an alkyl or a functional group. Either the Lewis acid- or the palladium-mediated reactions between acyl halides and (Z)-2 or (E)-2 are chemoselective but non-stereospecific. On the contrary, the palladium-mediated reaction between (Z)-3a (R = phenyl) and benzoyl chloride is stereospecific and affords the 1-sily ketone (E)-38 in a high yield. Finally, the configuration of the 1,2-disubstituted ethenyltrimethylsilanes synthesized during these studies has been unambiguously assigned by NMR spectroscopy.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
