Developing a transition-metal-free green protocol for the electrophilic hydrazination of silyl enol ethers using diazo electrophiles with EtOH–H₂O as a safe solvent

Abstract

We report a metal catalyst-free, HF-free and open-flask green protocol for the electrophilic hydrazination of enoxy silanes at an energy-efficient room temperature, taking advantage of the eco-safe EtOH–H2O solvent.

Promoting Catalytic C-Selective Sulfonylation of Cyclopropanols against Conventional O-Sulfonylation Using Readily Available Sulfonyl Chlorides

“…This result supports the generation of the β-homoenolate species 11c that can be trapped by azodicarboxylate electrophile 11a. 20,47 This result is consistent with the literature that the Cu(II) catalyst effectively promotes the ring cleavage of cyclopropanols to furnish the corresponding metalated βhomoenolate (e.g., 11c). 15,48−51 It is also known that the metalated homoenolate 11c can be susceptible to β-hydride elimination, which would deliver the enone byproduct 4b.…”

“…Under standard conditions, replacement of the electrophile 2a with the azodicarboxylate enophile 11a resulted in the formation of the Michael addition product 11b (Scheme , eq 3). This result supports the generation of the β-homoenolate species 11c that can be trapped by azodicarboxylate electrophile 11a . , This result is consistent with the literature that the Cu­(II) catalyst effectively promotes the ring cleavage of cyclopropanols to furnish the corresponding metalated β-homoenolate (e.g., 11c ). ,− It is also known that the metalated homoenolate 11c can be susceptible to β-hydride elimination, which would deliver the enone byproduct 4b . Accordingly, conducting the reaction with the exclusion of TsCl ( 2a ) resulted in the transformation of 1a to the enone 4b (eq 4, Scheme ).…”

A new synthetic approach to cyclic ureas through carbonylation using di-tert-butyl dicarbonate (boc anhydride) via one pot strategy

“…Furthermore, the incorporation of protected amine functionalities has been a common practice, 22 adding complexity. Some of the recent green methodology developments such as combination of EtOH–H 2 O and diazo electrophiles, 23 metal-free hydroalkoxylation, 24 visible-light catalysed raections, 25 aqueous mediated radical reactions 26 and umpolung of indoles with benziodoxol(on)e hypervalent iodine reagents 27 etc . have motivated us to initiate the development of an innovative, eco-conscious synthetic approach as a crucial component of our efforts in generating bio-active scaffolds.…”

Examining the Scope of Deriving β-Aryl Enones from Enol Silanes as Ketone Equivalents via Pd(II)-Mediated Sequential Dehydrosilylation and Arylation

“…The limited number of existing methods to transform saturated ketones to β-aryl enones and the limitations associated with these protocols spurred us to design and develop an alternative approach based on a retrosynthetic strategy relying upon silyl enol ethers as substrates, taking advantage of their function as masked enol equivalents of saturated ketones (Scheme ). In the forward synthetic direction, enol silanes would be expected to fulfill the role of acting as synthetic equivalents of saturated ketones by undergoing dehydrosilylation with the in situ generation of α,β-unsaturated ketones that would then be arylated in a one-pot process. − We were particularly interested in exploring silyl enol ethers as versatile reagents in a continuation of our earlier research that took advantage of their nucleophilic character to enable C–C and C–N bond formation with quinone, carbodiimide, and azodicarboxylate electrophilic systems. − Importantly, silyl enol ethers (a) are readily prepared from keto, aldehyde, and ester precursors; (b) are the reagents of choice for the regio- and stereo-selective generation of enolate equivalents; (c) undergo a diverse range of synthetic reactions, including aldol condensations, Michael additions, and [4 + 2] cycloadditions; and (d) find use as synthetic building blocks in pharmaceutical chemistry to generate drug-like compounds of diverse architecture. − Herein, we report for the first time the synthesis of β-arylated enone derivatives from enol silanes through the sequential generation of an enone in situ and the ensuing arylation with arylboronic acids or aryl halides in a convenient, one-pot process using modular Pd(II)/Pd(0) catalytic systems (Scheme , eq 3).…”