BF₃·Et₂O-Induced Decomposition of Ethyl 2-Diazo-3-hydroxy-3,3-diarylpropanoates in Acetonitrile: A Novel Approach to 2,3-Diaryl β-Enamino Ester Derivatives

Abstract

The BF(3).Et(2)O-induced decomposition of ethyl 2-diazo-3-hydroxy-3,3-diarylpropanoates, prepared by the addition of a series of benzophenones to ethyl diazo(lithio)acetate, is reported and studied. By using acetonitrile as a solvent, the corresponding N-acyl beta-enamino ester derivatives are obtained in good yields and with a diverse regioselectivity as the result of 1,2-aryl migration in the vinyl cation intermediates. The factors that govern the migratory aptitude as well as the mechanistic aspects of the reaction are discussed.

Metal‐Free Tandem Rearrangement/Lactonization: Access to 3,3‐Disubstituted Benzofuran‐2‐(3H)‐ones

“…With less reactive substrates or less Lewis acidic boranes (1a), similar compounds to 6 could be isolated and fully characterized as additional evidence for this intermediate (see the Supporting Information). [26] Reaction of 2g with either phenylboronic acid or with triphenylboraxine [27] resulted only in the insertion product 3q as determined by 1 HNMR spectroscopy. [25] Following mechanistic investigation, we turned our attention to the influence of the borane Lewis acid and nature of the ortho-substituted diazo derivative 2 in the tandem rearrangement/lactonization reaction to expand the substrate scope ( Table 2).…”

BF3·Et2O-Promoted Decomposition of Cyclic α-Diazo-β-Hydroxy Ketones: Novel Insights into Mechanistic Aspects

“…Herein, as a continuation of our interest in diazo chemistry [9,[22][23][24][25][26][27][28][29][30][31], we investigated the cascade rearrangement of destabilized vinyl cations deriving from the BF 3 •Et 2 O-induced decomposition of α-diazo-β-hydroxy ketones, prepared by aldol-type condensation of cyclic ketones with DAA (1). In particular, the effect of solvent and ring size on products distribution and mechanism paths were analyzed and discussed.…”

“…Indeed, also in this case, the adduct 26 derived from the solvent addition resulted to be the main reaction product (55%), while compounds 24 and 25 were isolated in 13% and 15% yields, respectively (Scheme 3). (29) were isolated in 26%, 36% and 16% yields, respectively, while adducts deriving from fluorine trapping were not observed (Scheme 4). Solventadducts, namely 1-(2-benzylcyclopent-1-en-1-yl)ethanone (30) and 1-(2-phenylcyclohex-1-en-1yl)ethanone (31); 1-cyclopentylidene-1-fluoropropan-2-one (32); and the inseparable mixture of 1-(2fluorocyclohex-1-en-1-yl)ethanone (33) and 1-cyclopentylidene-1-phenylacetone (34) were isolated using benzene as the solvent (Scheme 4).…”

“…Reaction of 1-diazo-1-(1-hydroxycyclohexyl)propan-2-one (22) with BF3•Et2O in n-pentane resulted again in a complex crude mixture whose purification allowed the exclusive isolation of 1-(2-hydroxycyclohept-1-en-1-yl)ethanone (35) in 12% yield (Scheme 5). When the same reaction was performed in acetonitrile, the enamino ketone 36 was obtained in 42% yield (29) were isolated in 26%, 36% and 16% yields, respectively, while adducts deriving from fluorine trapping were not observed (Scheme 4). Solvent-adducts, namely 1-(2-benzylcyclopent-1-en-1-yl)ethanone (30) and 1-(2-phenylcyclohex-1-en-1-yl)ethanone (31); 1-cyclopentylidene-1-fluoropropan-2-one (32); and the inseparable mixture of 1-(2-fluorocyclohex-1-en-1-yl)ethanone (33) and 1-cyclopentylidene-1-phenylacetone (34) were isolated using benzene as the solvent (Scheme 4).…”

Metallfreie Tandem‐Umlagerung/Lactonisierung: Zugang zu 3,3‐disubstituierten Benzofuran‐2‐(3H)‐onen

“…[26] Die Reaktion von 2g mit Phenylboronsäure oder mit Tr iphenylboraxin [27] führte nur zum Insertionsprodukt 3q,w ie mittels 1 H-NMR-Spektroskoopie bestimmt wurde. Wenn beispielsweise 2p (R = n-Hexyl) verwendet wurde,k onnte nur der entsprechende a-funktionalisierte Ester 3r als einziges Produkt in 59 %A usbeute isoliert werden, ohne dass eine Umlagerung stattfand.…”