Reactions of para-quinone methides (p-QMs) with α-diazo-β-ketosulfones
and their corresponding
esters as well as simple β-dicarbonyl compounds and β-ketosulfones
have been carried out under basic conditions. While the reaction of
diazosulfone with p-QMs afforded trisubstituted olefins
via deacylative 1,6-addition and elimination, α-diazo-β-ketoesters
and various active methylene compounds such as 1,3-dicarbonyls and
β-ketosulfones afforded tetrasubstituted olefins via 1,6-addition
and aerial oxidation. These simple, environmentally benign, and mechanistically
diverse protocols provided the products in moderate to excellent yields
and selectivities.
The reactivity of the Hauser−Kraus (H−K) donor, 3-sulfonylphthalide, with various activated imines under basic conditions is demonstrated. The reaction of 3-sulfonylphthalide with Boc-protected aldimine provides a rapid access to 1,2-imine adducts and alkylidenephthalides depending upon the stoichiometry of the base. The alkylidenephthalides could be transformed to ketophthalides, a new class of phthalides, on acid hydrolysis, which upon reductive cyclization using Zn/AcOH afforded the natural product homalicine. On the contrary, the Boc-protected isatinimines undergo an efficient H−K annulation to provide spiroisoquinolinone-oxindoles in excellent yields. However, the corresponding conjugated ketimines afforded Michael adducts, which were converted to the corresponding alkylidenephthalides under TBAF conditions. Article pubs.acs.org/joc
A protocol for the stereoselective synthesis of alkylidenephthalides and indanediones has been developed through the reaction of o-hydroxychalcones and their styrenyl analogues, respectively, with 3-sulfonylphthalide. The mechanism for the former synthesis involves Michael addition-E 2 elimination sequence, while the latter involves a [4 + 1] Hauser-Kraus annulation. The mechanistic studies reveal that the strategically positioned phenolic group plays a pivotal role in the observed reactivities. The alkylidenephthalides, which are latent 1,4dicarbonyl compounds, were further converted to triarylfurans under Paal-Knorr conditions in good to excellent yields. This protocol unravels several key features such as substrate specific product formation, namely, alkylidenephthalides from chalcones, and indanediones from vinylogous chalcones in their reaction with 3-sulfonylphthalide as well as the role of alkylidenephthalides as 1,4-dicarbonyl surrogates in Paal-Knorr furan synthesis.
Accessing homogenous glycoconjugates is of significance for assessing their biophysical activities and sometimes as vaccine candidate. Synthesis of glycoconjugates involves two species of which, glycosyl donor plays pivotal role in controlling the outcome of the glycosylation. Recently discovered alkynyl glycosyl carbonate donors possess self‐stability, high reactivity, and fast reaction time (15–30 min) when activated with [Au]/[Ag]‐catalysts. Herein, we report metal free conditions for the activation of the same alkynyl glycosyl carbonate donors using I2/TMSOTf in stoichiometric quantities. Extrusion product was characterized to be the vinylidene iodide by single crystal X‐ray analysis. The reaction conditions were illustrated to be suitable for synthesis of various glycosides, purine/pyrimidine nucleosides and a pentasaccharide repeating unit of Klebsiella pneumoniae (O‐3‐antigen).
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