Yuto Unoh

An Approach to Benzophosphole Oxides through Silver- or Manganese-Mediated Dehydrogenative Annulation Involving CC and CP Bond Formation†

Benzophosphole construction was achieved through the Ag(I) -mediated dehydrogenative annulation of phenylphosphine oxides with internal alkynes in a process involving CC and CP bond formation. A wide range of asymmetrical phenylacetylenes could be employed and the reactions proceeded with perfect regioselectivity. Moreover, the annulation could be conducted even at room temperature when a Mn(III) promoter was used in place of Ag(I) .

Rhodium(III)-catalyzed Oxidative Coupling through C–H Bond Cleavage Directed by Phosphinoxy Groups

A straightforward synthesis of phosphaisocoumarins is achieved by the rhodium-catalyzed oxidative coupling of diarylphosphinic and phenylphosphonic acid derivatives with alkynes. The P-OH groups effectively act as the key function for the regioselective C-H bond cleavage. Related oxidative coupling of phenylphosphine oxides with alkenes can also be conducted smoothly under similar conditions.

Rhodium(III)-catalyzed regioselective C-H alkenylation of phenylphosphine sulfides.

The regioselective alkenylation at the ortho position of phenylphosphine sulfides using alkenes proceeds efficiently in the presence of a cationic Cp*-rhodium(III) catalyst and an appropriate oxidant. A similar rhodium catalyst also promotes the redox-neutral coupling of the phosphine sulfides with alkynes to afford ortho-alkenylated products.

Rhodium(III)-catalyzed oxidative alkenylation of 1,3-dithiane-protected arenecarbaldehydes via regioselective C-H bond cleavage.

A Rh(III)-catalyzed direct alkenylation of 2-aryl-1,3-dithiane derivatives with alkenes has been developed. The 1,3-dithiane group can serve as an effective directing group for the exclusively monoselective alkenylation under mild oxidative conditions. The directing group is readily removable after the coupling event.

Regioselective Synthesis of Benzo[b]phosphole Derivatives via Direct ortho-Alkenylation and Cyclization of Arylthiophosphinamides.

A new regioselective synthetic methodology for benzo[b]phosphole derivatives has been developed. Thus, a range of functionalized benzo[b]phosphole oxides could be synthesized via Rh(III)-catalyzed C-H alkenylation of arylthiophosphinamides with alkynes followed by formal phospha-Friedel-Crafts cyclization.

Palladium-catalyzed decarboxylative arylation of benzoylacrylic acids toward the synthesis of chalcones.

It has been found that readily available 3-benzoylacrylic acids undergo palladium-catalyzed decarboxylative arylation with arylboronic acids in the presence of a copper salt oxidant to produce chalcone derivatives. The decarboxylative arylation could also be achieved using aryl halides as the alternative aryl source to expand the applicable scope.

Synthesis of Benzo[c]thiophenes by Rhodium(III)-Catalyzed Dehydrogenative Annulation

The dehydrogenative annulation of thiophen-2-carboxamides with 2 equiv of alkynes proceeds efficiently in the presence of a rhodium catalyst and a copper oxidant to furnish multiply substituted benzo[c]thiophenes. Some of the synthesized benzo[c]thiophenes exhibited strong solid-state fluorescence.

1,2-Thiazines: One-Pot Syntheses Utilizing Mono and Diaza Analogs of Sulfones.

A one-pot Michael addition/cyclization/condensation reaction sequence for the regioselective synthesis of 1,2-thiazines, starting from propargyl ketones and NH-sulfoximines or NH-sulfondiimines, has been developed. Under mild and operationally simple reaction conditions previously unprecedented 1,2-thiazine 1-imide and 1-oxide derivatives are formed in good to excellent yields. The products represent heterocyclic building blocks, readily modifiable by a regioselective C-H bond functionalization, classical cross-coupling reactions, and deprotection.

Metal-Free Electrophilic Phosphination/Cyclization of Alkynes

A metal-free electrophilic phosphination reaction has been developed. Electrophilic phosphorus species generated in situ from secondary phosphine oxides and Tf2O smoothly couple with alkynes possessing pendant nucleophiles to afford the corresponding phosphinated cyclization products in good yield. Preliminary NMR studies show that phosphirenium species may be involved as intermediates of the cyclization reactions.

Phosphenium-Cation-Mediated Formal Cycloaddition Approach to Benzophospholes

A phosphenium-cation-mediated formal [3+2]-cycloaddition reaction of internal alkynes is reported. The reaction proceeds under metal-free conditions to give the corresponding C-P rearranged benzophospholes regioselectively, even when ortho- and para-substituted arylphosphine oxides are starting substrates. Mechanistic studies by 31 P{1 H} NMR analysis suggest an involvement of three-membered phosphirenium cation species and C-P rearrangement prior to a ring closure for benzophosphole skeleton formation.