Reactivity of Allenylphosphonates and Allenylphosphine Oxides Toward 9‐Chloroacridines and Acridone — A Facile Route to New N‐Substituted Acridones.

Base-mediated addition of acridones to allenylphosphonates/allenylphosphine oxides (OCH2CMe2CH2O)P(O)CH=C=CR1R2 {R1 = R2 = Me (1), R1 = R2 = [ $-{\rm CH}_{2^-}$ ]5 (2)}, Ph2P(O)C(H)= C=CR1R2 {R1 = R2 = Me (3), R1 = R2 = [ $-{\rm CH}_{2^-}$ ]5 (4)} and (EtO)2P(O)C(H)=C=CMe2 (5) in DMF results in the regiospecific formation of phosphono-acridones and acridonylphosphine oxides. The acridone addition products were also obtained in the reaction of allenes 1 and 2 with 9-chloroacridine under [Pd]-catalysed conditions, along with (unexpected) α-acridinyl substituted allenes. In contrast, 9-benzyl-6-chloro-purine reacted with 1 affording a β-substituted purinone phosphonate. Allenes 1–2 did not react with acridones in the absence of base (CsF), but in the presence of Pd(OAc)2/DMF (or DMA)/pivalic acid rearranged to give 1,3-butadienes probably via [Pd]-allyl complexes. The phosphono-acridones were amenable to Horner–Wadsworth–Emmons (HWE) reaction and led to N-substituted acridones. Key products have been characterized by single-crystal X-ray crystallography.