Remove contents from tin … Thiol esters have been successfully synthesized through tin-free radical carbonylation (see scheme; V-40=initiator). This approach can be further extended to sequential radical reactions involving cyclization, carbonylation, and trapping of acyl radicals by phenyl benzenethiosulfonate.
Catalytic [2 + 2 + 1 + 1] cocyclization reaction of an alkyne, an alkene, and two molecules of carbon monoxide, leading to functionalized hydroquinones, was studied. Using [Cp*RuCl2]2 as a catalyst, we found that a variety of electron-deficient alkenes, such as α,β-unsaturated ketones, esters, amides, and nitriles, can be employed as an alkene coupling partner to give the corresponding hydroquinones.
Acyl cyanides have been prepared by the three-component coupling reactions comprised of alkyl allyl sulfones, carbon monoxide, and p-tolylsulfonyl cyanide under tin-free radical reaction conditions.
A quadraphasic phase-vanishing method was developed that employs water as the fourth phase acting as an ‘acid scavanger phase'. This protocol worked well for bromination of acetophenones giving high yields of the corresponding α-bromo ketones.
An efficient one-pot sequence comprising a PRE-mediated radical 5-exo-cyclization, a radical carbonylation, a nitroxide trapping reaction, and a subsequent acid-catalyzed Friedel−Craft-type acylation provides a new entry into 3,4-cyclopenta-1-tetralones. Eight examples are presented.
Ketone α,δ-dianions are generated by vinylogous extension of ketone α,β-dianions with alkenes such as vinylarenes, vinylsilanes, and vinyl sulfides, which then undergo reactions at the δ and α positions with different electrophiles, creating ketone frameworks. This work represents a cascade-type anion method that achieved three- and four-carbon component assembly reactions leading to ketones.
Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-ζ pseudopotential (DZP) basis set, with (QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional methods (BHandHLYP, B3LYP) predict that α,β-unsaturated acyl radicals and α-ketenyl radicals exist as isomers. At the CCSD(T)/cc-pVDZ//BHandHLY/cc-pVDZ level of theory, energy barriers of 15.1 and 17.7−21.7 kJ mol-1 are calculated for the isomerization of s-trans-propenoyl and s-trans-crotonoyl radical to ketenylmethyl and 1-ketenylethyl radical, respectively. Similar results are obtained for the reactions of s-trans isomers involving silyl, germyl, and stannyl groups with energy barriers (ΔE‡) of 12.2−12.4, 13.1−13.9, and 12.9−18.2 kJ mol-1 at the CCSD(T)/DZP//BHandHLYP/DZP calculation, respectively. These results suggest that α,β-unsaturated acyl radicals and α-ketenyl radicals are not canonical forms but are isomeric species that can rapidly interconvert.
A convergent synthesis of α-methylene amides exploits a hybrid radical/ionic concept in which radical carbonylation of alkynes is followed by ionic trapping of the resulting carbonyl-containing radical species with amines (see scheme). The reaction of substituted terminal alkynes with pressurized CO, Bu3SnH, and 2,2′-azobisisobutyronitrile in the presence of a large excess of amines gave good yields of the corresponding α-methylene amides.
Ketone dilithio α,β- and α,β′-dianions can be generated by a tin–lithium exchange reaction of the lithium enolate of β-tributyltin substituted ketones. A chelation-aided approach, which employs β-dichlorobutyltin substituted ketones and n-BuLi, is also useful for the generation of ketone α,β-dianions having the Z-geometry at the alkene. The generated dianions can be transformed into substituted ketones by reaction with various carbon electrophiles.