Visible Light Mediated Organophotoredox Catalyzed Synthesis of Tetraketones Using Tertiary Amines as Alkyl Synthons.

Eosin Y catalyzed syntheses of bioactive tetraketones using cyclic-1,3-diketones and tertiary amines as alkyl synthons under 18 W blue LED have been accomplished. The condition is very mild that uses air as a green oxidant and avoids previously used harsh conditions like high temperature. Diverse arrays of tertiary amines first undergo reductive quenching of excited photocatalysts to form iminium ions that upon subsequent attack by cyclic-1,3-diketones give rise to tetraketones. This method is demonstrated with 31 examples with yields up to 76%. The feasibility of this reaction in the presence of eosin Y catalyst under a solar condition is also demonstrated with significant examples.

Catalyst-Assisted Selective Vinylation and Methylallylation of a Quaternary Carbon Center Using tert-Butyl Acetate.

The In(OTf)3-catalyzed α-vinylation of various hydroxy-functionalized quaternary carbon centers using in situ generated isobutylene from tert-butyl acetate is presented as a novel synthetic methodology. Moreover, tert-butyl acetate is a nonflammable feed stock and is a readily available source for the in situ production of vinyl substituents, as demonstrated by the vinylation reaction with quaternary hydroxy/methoxy compounds. Moreover, an excellent selectivity for methylallylation over vinylation was obtained with Ni(OTf)2 as a catalyst. In the case of peroxyoxindole, methylallyl-functionalized 1,4-benzoxazin-3-one derivatives were formed through the sequential rearrangement of peroxyoxindole followed by the nucleophilic attack by isobutylene. The detailed mechanism for this reaction and rationalization for the selectivity are provided using kinetics and density functional theory studies.

Continuous-Flow Direct Azidation of Alcohols and Peroxides for the Synthesis of Quinoxalinone, Benzooxazinone, and Triazole Derivatives.

Continuous-flow reactors provide an ideal tool for the synthesis of potentially explosive but synthetically useful organic substances like organic azides due to their intrinsically small volume leading to very effective collision and highly controlled reaction conditions. Herein, we report the continuous-flow direct azidation of various alcohols by using TMSN3 as an azide transfer reagent in the presence of Amberlyst-15 as a recyclable catalyst. Numerous 3-hydroxy-2-oxindoles effectively undergo azide transfer to afford azide-functionalized quaternary stereocenters in a continuous-flow module. Interestingly, peroxyoxindole undergoes sequential skeletal rearrangement to generate a carbocation followed by nucleophilic azidation to afford a library of substituted 2-azido-2H-benzo[b][1,4]oxazin-3(4H)-one derivatives under continuous flow. Furthermore, a continuous-flow Cu-catalyzed click reaction afforded triazole-functionalized deivatives. Next, reduction of azide in the presence of PPh3 affords the amine derivatives in good yields. The continuous-flow application was extended further for the thermolytic skeletal rearrangement of 3-azide-2-oxindole for the synthesis of biologically important quinoxalin-2(1H)-ones without any reagents. Furthermore, this continuous-flow direct azidation reaction is scaled up to 6.144 g of azides with a turnover number of 9.24 under safer conditions.