An Activated Germanium Metal-Promoted, Highly Diastereoselective Reformatsky Reaction

Abstract

Activated germanium metal, prepared by the reduction of germanium(II) iodide with potassium metal, was found to promote the Reformatsky reaction effectively under mild conditions. In the presence of activated germanium metal, the reactions of alpha-bromo ketones 2a and 2b and alpha-bromo imides 2e and 2f with benzaldehyde (1a) proceeded smoothly to give the corresponding beta-hydroxy carbonyl compounds 3a, 3b, 3e and 3f, respectively, in good yields and with good syn diastereoselectivity. The activated germanium metal-promoted, asymmetric Reformatsky reaction of enantiomerically pure-oxazolidinone derivatives 2g-j with various aldehydes 1a-d was also examined; the highest diastereoselectivity was achieved when (1S,2R)-2-amino-1,2-diphenylethanol-derived 2j was used as the Reformatsky donor. The excellent diastereoselectivity could be explained in terms of the formation of a chairlike, six-membered transition state between the aldehyde and enolate as in the Zimmerman-Traxler model. A single recrystallization of the Reformatsky adducts, followed by hydrolysis and subsequent esterification, led to enantiomerically pure methyl 3-hydroxy-2-methylalkanoates 10j-m, with almost quantitative recovery of the enantiomerically pure 2-oxazolidinone 14.

Selective Direct Synthesis of Organofunctionalized Dialkylgermanes from Solvochemically Activated Germanium

“…The reactions described in this work require the use of the orange‐colored, amorphous germanium that is obtained in the reduction of GeCl 2 ⋅dioxane (or of GeI 2 ) with Li[Et 3 BH]. Previously reported black activated germanium, which can be obtained from GeI 2 and elemental potassium,13 did not react with the alkyl bromides used in this work under the given reaction conditions (Table 1), although it reacts with α ‐haloesters and other Reformatsky substrates at room temperature 13. Brown amorphous germanium, which was obtained from GeCl 4 and lithium naphthalide, did not show a reactivity analogous to the one of the orange material either.…”

Selektive Direktsynthese funktionalisierter Dialkylgermane aus lösungschemisch aktiviertem Germanium

“…Die hier beschriebenen Reaktionen erfordern die Verwendung des orangefarbenen amorphen Germaniums, wie es bei der Reduktion von GeCl 2 ⋅Dioxan (oder auch von GeI 2 ) mit Li[Et 3 BH] entsteht. Das bereits beschriebene schwarze, aktivierte Germanium, das bei der Umsetzung von GeI 2 mit elementarem Kalium entsteht, zeigt unter den in Tabelle 1 genannten Bedingungen keine Reaktion mit den Alkylbromiden, obwohl es mit α ‐Halogenestern und anderen Reformatsky‐Substraten schon bei Raumtemperatur reagiert 13. Auch das durch Reduktion von GeCl 4 mit Lithiumnaphthalid entstehende braune, amorphe Germanium verhält sich nicht wie das orangefarbene Produkt.…”

First Isolation and Characterization of the Highly Coordinated Group 14 Enolates: Effects of the Coordination Controls on the Geometry and Tautomerization of Germyl Enolates

“…In contrastt ot he active research on silyl or stannyl enolates, the study of germyl enolates has been limited to their use as synthetic reagents. [16] The cross-aldol [17] and Mannich [18] reactions that are mediated by ar eduction of a-halo carbonyls using germanium(II) salts are evidence of the generation and handys tability [17b] of germyle nolates, whichp rompted us to use germaniumtoi nvestigatet he structure and tautomeric behavioro ft he Group 14 metale nolates. In this study,w er eport the generationo fg ermyl enolates from an a-halo ketone.…”