Phosphinines synthetic approaches

Several independent synthetic approaches to 1,22 -, 1,32 - and 1,41 -azaphosphinines (12)-(14), as well as 12 32 -diphosphinins (15) and U 32 52 -triphosphinins (16), have been published. Synthetic work on polyhalogenated aza-2 -phosphinines, e.g. (17), has been carried out, mainly by Russian research groups.. ... 

Abstract Recent developments in the chemistry of phosphinines are reported. This chapter presents and discusses the most important breakthroughs achieved during the last decade. New synthetic approaches allowing the synthesis of polyfunctional phosphinines as well as improvements of well known methods are reported. The use of phosphinines in coordination chemistry is also presented with particular emphasis on their use in the stabilization of low valent and highly reduced transition metal complexes. Another aim of this review is to discuss recent applications of phosphinines, and structures derived directly from phosphinines such as phosphacyclohexadienyl anions and phosphabarrelenes, as ligands in homogeneous catalysis. 

Diels-Alder reaction at higher temperature (around 110-120 °C) to give azaphos-phabarrelenes 38 which finally decompose to yield the expected 2,3,5,6-tetrafunc-tional phosphinines 39. Importantly, the difference of reactivity between diaza and mono aza-phosphinine derivatives allows the successive use of two different alkynes. The general principle of this synthetic approach is presented in Scheme 10. It is important to mention that all these cycloaddition/cycloreversion sequences can be performed in the same flask and there is no need to isolate the 2-zaphosphinine formed after the first Diels-Alder reaction. 

A synthetic approach toward 3,5-disubstituted phosphinines such as 68 was reported in 2008 [42], This simple approach relies on the protodesylilation of 2,6-bis(trimethylsilyl)phosphinines (such as 67) with HC1 in ether (Scheme 16). A DFT study revealed that protonation first takes place at the phosphorus atom and that a chloro-l,2-dihydrophosphinine is involved as intermediate. 

Interest in the synthesis and reactivity of the six-membered, potentially aromatic, phosphinine ring system has also continued, but at a much lower level than in recent years. New synthetic work includes the application of the pyrylium salt route to phosphinine synthesis, this time starting from pyrylium salts bearing chiral substituents to give the related chiral phosphinines," and the development of new routes to the 2-phosphanaphthalene (137)" ° and the phosphinine-2-aldehyde (138). Also reported is an approach to the synthesis of l,2-dihydro-l,4,2-benzo-diazaphosphinines," cationic gold(I) complexes of 2,4,6-tri-t-butyl-l,3,5-triphosphabenzene," and the synthesis of some X -phosphinines from phosphonium-iodonium ylides." " ... 

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