Metallsubstituierte Carbene und C‐metallierte Diazoalkane, VI¹⁾ α‐Diazo‐β‐hydroxy‐carbonsäureester und ‐ketone aus Carbonyl‐ und Diazolithioverbindungen sowie ihre Umlagerung zu β‐Ketocarbonsäureestern und β‐Diketonen

Abstract

Diazoessigsaure-athylester (1 a) ist rnit Butyllithium bei -65 bis -110°C (in Tetrahydrofuran) in Diazolithioessigsaure-athylester (2a) umwandelbar, welcher rnit den Carbonylverbindungen 3 die a-Diazo-P-hydroxycarbonsaureester 4 liefert. Diese sind auch in situ aus l a und 3 rnit Butyllithium zuganglich. Sie lassen sich protonenkatalysiert in die P-Ketocarbonsaureester 19 umlagern. Bei Cycloalkanonen entspricht dies einer Ringerweiterung. -Aus den Diazoketonen l b -e erhalt man die a-Diazo-P-hydroxyketone 5-8, indem man sie bei ca. -70°C im Gemisch rnit den Carbonylverbindungen 3 rnit Lithiumdiisopropylamid umsetzt. Butyllithium ist hier als Metallierungsmittel ungeeignet. Wie sich rnit den Verbindungen 5 ergab, werden a-Diazo-P-hydroxyketone protonenkatalysiert in unterschiedlichem AusmaB zu P-Diketonen umgelagert oder in einer Retroaldolreaktion zu Carbonylverbindungen 3 und Diazoketonen gespalten.Metal-substituted Carbenes and C-metalated Diazoalkanes, VI1). -a-Diazo-P-hydroxy-carboxylates and -ketones from Carbonyl and Diazo Lithio Compounds and their Rearrangement into P-Ketocarboxylates and f3-Diketones Ethyl diazoacetate (la) can be metalated with butyllithium in tetrahydrofuran at -65°C to -110°C to give ethyl diazolithioacetate (2a), which reacts with the carbonyl compounds 3 to give (after hydrolysis) the a-diazo-P-hydroxycarboxylates 4. These can also be obtained more conveniently, by in situ reaction of 1 a and 3 with butyllithium (-65"C, tetrahydrofuran). On treatment with hydrogen chloride the compounds 4 rearrange (with loss of nitrogen) to the P-ketocarboxylates 19. In the case of cycloalkanones this sequence represents a ring enlargement. -The a-diazo-P-hydroxyketones 5-8 are formed when a mixture of the carbony1 compounds 3 and the diazoketones l b -e is treated (in tetrahydrofuran, -65°C) with lithium diisopropylamide. Butyllithium is not suitable as metalating reagent. As in the case of compounds 5, on treatment with acids a-diazo-P-hydroxyketones suffer partial rearrangement to P-diketones (with loss of nitrogen) and partial retro-aldol reaction to 3 and diazoketones.*) Korrespondenz bitte an diesen Autor richten. **) Herrn Prof. H. Bredereck rnit den besten Wiinschen zum 70. Geburtstag gewidmet.

Ethyl Lithiodiazoacetate: Extremely Unstable Intermediate Handled Efficiently in Flow

“…An attempt to increase the temperature slightly to −72 °C did not improve the yield of the reaction product 4 any further (Table , entry 5). The yield of 4 obtained in the optimized flow process (62 %) is higher than in the batch protocol reported previously (50 %) …”

“…[15] In this set-up, LDA was generated in af irst reactor (R1) at room temperature within one minutea nd then cooled to À78 8C( C1). [16] With the optimized reactionc onditions in hand (Table 1, entry 4), the scope of ketones for the addition of 2 was investigated. The ethyl lithiodiazoacetate (2)was then immediately trapped by ap recooled(in coil C3) solution of the elec- (2) trophile in the reactor R3.…”

Boranes in Organic Chemistry 1. α-Carbonylalkyl- and β-Oxyalkylboranes in Organic Synthesis

“…Schöllkopf et al [13] have been studied reactions of α-diazo-β-hydroxy-carboxylates and α-diazo-β-hydroxy-ketones with diazo compounds and their rearrangement into β-ketocarboxylates and β-diketones. 2-Chlorobenzo[1,3,2]-dioxaborole reacted at -110°C in dichloromethane with stannum and/or silicon derivatives ethyl diazoacetate to form ethyl benzo[1,3,2]-dioxaborol-2-yl-diazo-acetate 13 (Scheme 7a).…”

Reações de inserção intramolecular de diazo compostos polifuncionais catalisadas por ródio(II): síntese de oxetan-3-ona-2-carboxilato e outros heterociclos funcionalizados

“…Um método para a construção de compostos α-diazo carbonilados que tem recebido especial atenção envolve modificações químicas com retenção da função diazo, particularmente via reações de metalação 7,[9][10][11][12][13][14][15] . Por exemplo, a preparação de uma grande variedade de α-diazo-β-cetoésteres 1 pode ser convenientemente efetuada, a partir da reação entre o mercurial diazo éster 2 16,17 e haletos de ácidos, em condições essencialmente neutras (Esquema 1) 18 .…”