The compounds S(6-t-Bu-4-Me-C₆H₂O)₂P(O)Cl (1), CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(O)Cl (2) and (2,2′-C₂₀H₁₂O₂)P(O)Cl (3) react with diazabicycloundecene (DBU) to give rise to, predominantly, the phosphonate compounds [S(6-t-Bu-4-Me-C₆H₆O)₂P(O)(DBU)]⁺[Cl]⁻ (4), [CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(O) (DBU)]⁺[Cl]⁻ (5) and [(2,2′-C₂₀Hi₂O₂)P(0)(DBU)]⁺[Cl]^- (6). The first two compounds could be isolated in the pure state. In analogous reactions of 1 and 2 with diazabicyclononene (DBN) or N-methyl imidazole, only the pyrophosphates [S(6-t-Bu-4-Me-C₆H₂O)₂P(O)]₂O (7) and [CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(O)]₂O (8) could be isolated, although the reaction mixture showed several other compounds in the phosphorus NMR. A possible pathway for the formation of phosphonate salts is proposed. The X-ray crystal structures of4,7 and8 are also discussed.

The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated acetylenes with P^III compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC₆H₃O)P (μ-N-t-Bu)₂P⁺[(NH-t-Bu)N[(CO₂]-i-Pr)(HNCO₂-i-Pr)]](Cl^-)(2-t-Bu-4-MeC₆H₃OH)(23)and [CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(O)C(CO₂Me)C-(CO₂Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction.

Synthesis, structures and stability (thermal and air) of allenylphosphonates of the type (OCH₂CMe₂CH₂O)P(O)C(R)=C=CR'R" and [R"R'C=C=C(R)P(O)(OCH₂)₂]₂C are discussed. Thermally activated dimerization (cycloaddition) of (OCH₂CMe₂CH₂O)P(O)C(H)=C=CMe₂ leads to the phosphonocyclobutane [(OCH₂CMe₂CH₂O)P(O)C(H)=]₂[C-CMe₂]₂ (18). Many of these allenes undergo addition of diethylamine to lead to enaminophosphonates that are readily hydrolysed by water to lead to 𝛽-ketophosphonates. The latter compounds are useful as Horner-Wadsworth-Emmons (HWE) reagents. Molecular structures of (OCH₂CMe₂CH₂O)P(O)C(CH₂OH)=C=CH₂ (6), [H₂C=C=C(H)P(O)(OCH₂)₂]₂C (9), (OCH₂CMe₂CH₂O)P(O)CH=C=CH₂ (12), [(OCH₂CMe₂CH₂O)P(O)C(H)=]₂[C-CMe₂]₂ (18), and the 𝛽-ketophosphonate (OCH₂CMe₂CH₂O)P(O)CH₂)-C(O)CHMe₂ (24) have been determined. In compound 6, intermolecular hydrogen bonding between the phosphoryl oxygen and the hydroxyl group leading to an infinite chain is observed. In 6, there is a significant deviation (ca 7°) from the orthogonality expected between the planes containing 4 atoms of (a) H₂C=C and (b) C=C(H)P in the allene part. In 9, weak C-H…O interaction between the phosphoryl oxygen atom and a CH₂ proton of the six-membered ring is present.

Synthesis and X-ray structure of a new bismuth dipicolinate cooordination polymer, {[Bi((2,6-O₂C)₂C₅H₃N)((2-HO₂C-6-O₂C)C₅H₃N)(H₂O)]₂.5H₂O}$_n$ (7) are presented. Compound 7 has dimeric units with a Bi₂O₂ skeleton that are linked by additional weak Bi-O interactions leading to a polymeric structure. The overall coordination number at bismuth is 9 [two Bi-N and seven Bi-O bonds]. New routes to a second crystalline modification (4′) of the previously reported coordination polymer, bismuth tris(picolinate), [Bi(2-O₂C-C₅H₄N)₃]$_n$ (4), are described; bond parameters in the two crystalline forms (4 and 4′) are compared. In both the compounds 4′ and 7, bismuth has a distorted tricapped trigonal prismatic geometry.

Base-mediated addition of acridones to allenylphosphonates/allenylphosphine oxides (OCH₂CMe₂CH₂O)P(O)CH=C=CR¹R² {R¹ = R² = Me (1), R¹ = R² = [−CH₂−]₅ (2)}, Ph₂P(O)C(H)=C=CR¹R² {R¹ = R² = Me (3), R¹ = R² = [−CH₂−]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.

Phosphano-indoles were synthesized in a fairly straightforward route from the reaction of simple cyclodiphosphazanes [XP(𝜇-N-t-Bu)₂PY] [X=Y=NH-$t$-Bu (1a); X=Y=NH-i-Pr (1b)] with o-aminophenyl functionalized propargyl alcohols. The reaction occurs via an allene intermediate formed by P^III-O-C$\to$P^V(O)-C rearrangement, followed by cyclization utilizing the central allenic carbon and the –NH₂ functionality. In a similar way, cyclodiphosphazanes [XP(𝜇-N-t-Bu)₂PY] [X=Y=Cl (1c); X=Cl, Y=NH-t-Bu(1d)] have been treated with N-hydroxy substrates to obtain novel P^III-O-N$\to$P^V(O)-N rearranged products.X-ray structures of the four products, 2-(1-phenyl-ethyl)-3-[(t-Bu)NH)P(𝜇-N-t-Bu)₂P(O)]-indole [14], cis-{[-C(=O)-C₆H₄-C(=O)-]-N-P(=O)-N-t-Bu}₂[cis-18], trans-{[-C(=O)-C₆H₄-C(=O)-]-N-P(=O)-N-t-Bu}₂ [trans-18] and cis-[(t-BuNH)P(𝜇-N-t−Bu)₂P(=O)-N{-C(=O)-CH₂-CH₂-C(=O)-}] [cis-19] are also reported

Electrophilic allylation of phenolic substrates including salicylaldehydes with (𝛼-hydroxy) allylphosphonates is presented. It is observed that catalytic FeCl₃ is sufficient to accomplish the allylation. Interestingly, the reaction led to the formation of allylphosphonates in addition to vinylphosphonates, depending upon the substituent. The vinylphosphonates obtained here are 𝐸-isomers. More importantly, the reaction occurred regioselectively with respect to the phenolic substrates. Substituted allylphosphonates are formed when salicylaldehyde or (2-hydroxy-phenyl)arylmethanones are used. Conclusive proof for the formation of allylphosphontates as well as vinylphosphonates has been provided by single crystal X-ray crystallography.