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 selfdimerization-cum-cyclization of alpha-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc)2in the presence of PPh3 and Et3N . This reaction involves [4 + 2]-cycloaddition with the (beta,gamma) double bond of one allene as the dienophile; the double bonds at the alpha-aryl-(beta ',gamma ') group and (alpha,beta)-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 3,6diphenylpyridazines 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.

Automated summary

In this study, phosphorus-based naphthalenes were synthesized through a series of reactions. Using Pd(OAc)2 as a catalyst, alpha-aryl allenylphosphonates or allenylphosphine oxides were self-dimerized and cyclized. Additionally, a [Pd] complex was obtained by reacting allenylphosphine oxides with Pd(OAc)2 in the presence of PPh3/Ag2CO3, and it could be used as a catalyst for C-C bond-forming reactions of phosphorus-based allenes with 2-iodophenol. Densely substituted 3,6-diphenylpyridazines were successfully synthesized through a thermally induced regioselective Inverse Electron Demand Diels-Alder (IEDDA) reaction and a [1,3]-H shift.