Substituent-dependent [4+2] or [2+2] cycloadditions of phenylallenyl phosphine oxides with arynes

A [4+2] cycloaddition strategy to assemble phenanthren-9-yldiphenylphosphine oxides is reported. This reaction relies on the strategic use of readily available phenylallenyl phosphine oxides as dienes to participate in [4+2] cycloaddition with arynes. Notably, benzo[b][1,4]oxaphosphinin-4-iums can be controllably synthesized by simply tuning the substituents in the phosphine oxide unit through a [2+2] cycloaddition cascade.

Divergent Reactivity of Phosphorylated and Related Allenes: [4 + 2] Cycloaddition with 3,6-Diphenyltetrazine, Self-Addition Leading to Dimers and [Pd]-Complex Formation

Phosphorus-based naphthalenes are formed by self-dimerization-cum-cyclization of α-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc)₂in the presence of PPh₃ and Et₃N . This reaction involves [4 + 2]-cycloaddition with the (β,γ) double bond of one allene as the dienophile; the double bonds at the α-aryl-(β',γ') group and (α,β)-carbons of the second allene act as the diene part. A subsequent proton shift also takes place. Upon treating allenylphosphine oxides with Pd(OAc)₂ [stoichiometry 2:1] in the presence of PPh₃/Ag₂CO₃, a [Pd]-complex is isolated and structurally characterized. This complex can be used as a catalyst for C-C bond-forming reactions of phosphorus-based allenes with 2-iodophenol. Densely substituted 3,6-diphenylpyridazines are conveniently obtained in excellent yields by a thermally induced regioselective Inverse Electron Demand Diels-Alder (IEDDA) reaction of allenes with 3,6-diphenyltetrazine, followed by a [1,3]-H shift.

Base catalysed intermolecular cyclisation of N-protected o-amino benzaldehyde/acetophenone with phosphorus/sulphur based allenes: facile synthesis of substituted quinolines

Base catalyzed reaction of N-Bz protected o-aminobenzaldehyde with allenylphosphonates affords O-phosphorylated quinolines via a route involving a thermal rearrangement.

Dual rhodium/copper catalysis: synthesis of benzo[b]fluorenes and 2-naphthalenylmethanones via de-diazotized cycloadditions

A novel synergistic rhodium/copper catalysis has been established, enabling de-diazotized cycloadditions toward the selective formation of benzo[b]fluorenes and 2-naphthalenylmethanones.

Synthesis of 1,4-dihydrophosphinoline 1-oxides by acid-promoted cyclization of 1-(diphenylphosphoryl)allenes

Phosphonoallenes in Brønsted acids (TfOH, FSO₃H, H₂SO₄) gave the corresponding 1,2-oxaphosphol-3-enium ions, that were studied by means of NMR and DFT calculations.

Regioselective carboannulation of electron-deficient allenes with dialkyl (2-formylphenyl)malonates leading to multisubstituted naphthalenes

A regioselective carboannulation of allenoates (or allenylphosphonates) with dialkyl 2-(2-formylphenyl)malonates leads to multi-substituted naphthalenes via Michael addition, cyclisation, dealkoxycarboxylation and tautomerisation.

Acid-promoted transformations of 1-(diphenylphosphoryl)allenes: synthesis of novel 1,4-dihydrophosphinoline 1-oxides

1-(Diphenylphosphoryl)alka-1,2-dienes in acids (TfOH, FSO₃H, H₂SO₄) give (3-hydroxyalk-1-en-1-yl)diphenylphosphine oxides, that are further converted into 1-phenyl-1,4-dihydrophosphinoline 1-oxides. The latter compounds are directly formed from these 1,2-dienes under the action of AlCl₃.

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

A range of phosphinoylindoles was prepared in one-pot from functionalized propargyl alcohols and a suitable P(III) precursor via a base-mediated reaction. The reaction proceeds via the intermediacy of allenylphosphine oxides. Similarly, phosphinoylisocoumarins were prepared from allenylphosphine oxides in a trifluoroacetic acid-mediated reaction; the latter also acts as a solvent. Interestingly, in the presence of wet trifluoroacetic acid, in addition to phosphinoylisocoumarins, phosphorus-free isocoumarins were also obtained. Key products were characterized by single crystal X-ray crystallography.

To stay as allene or go further? Synthesis of novel phosphono-heterocycles and polycyclics via propargyl alcohols

Novel (tetrahydro)dibenzazepines, N-hydroxyindolinones and polycyclic compounds are generated by a simple reaction of a chlorophosphite with functionalized propargyl alcohols.