Enolboration of conjugated ketones and synthesis of beta-amino alcohols
and boronated alpha-amino acids*
M. Zaidlewicz, W. Sok�l, A. Wolan, J. Cytarska, A. Tafelska-Kaczmarek,
A. Dzielendziak, and A. Prewysz-Kwinto
Department of Chemistry, Nicolaus Copernicus University,
87-100 Torun, Poland
Abstract: Enolization�aldolization of conjugated ketones, enantioselective
synthesis of benzofuryl beta-amino alcohols, and synthesis of p-dihydroxyborylphenylalanine
(BPA) and its analogs are described. Aldolization of benzaldehyde with
lithium dienolates derived from unhindered conjugated cyclohexenones
favored anti- selectivity, whereas syn selectivity was favored for hindered
cyclohexenones. Anti-aldols were preferentially formed from dienolborinates
derived from conjugated cyklohexenones, however,competing aldolization
at the 2-position was observed for hindered ketones. Benzofuryl beta-amino
alcohols were prepared using as a key step the enantioselective reduction
of the corresponding alpha-bromoacetylbenzofurans with (�)-B-
-chlorodiisopinocampheylborane. Ionic liquids were used as solvents
for the synthesis of BPA by the Suzuki cross-coupling reaction. The
reaction time is short, and a solution of the catalyst in the ionic
liquid can be recycled.
*Lecture presented at the XIth International Meeting
on Boron Chemistry (IMEBORON XI), Moscow, Russia, 28 July - 2 August
2002. Other presentations are published in this issue,
pp. 1157-1355.
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