Phosphinines derivatives

Phosphinine Derivatives and their Use as Versatile Intermediates in P-Heterocyclic... 

The first phosphinine derivative was synthesized by Markl in 1966, and the parent unsubstituted phosphinine itself was first reported by Ashe. The... 

After the first synthesis of a P-phosphinin derivative, the 2,4,6-triphenyl compound (1) <66AG(E)846>, and the isolation of the unsubstituted phosphinin (2) <7UA3293>, a dramatic development and an avalanche of publications followed. 

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 remarkable and valuable reaction takes place when aromatic acid chlorides are reaeted with phospholes and the mixture then treated with water. The products possess the 1,2-dihydrophos-phinine ring structure. Apparently the nucleophilic phosphorus displaces chlorine from the acid chloride water then adds to the phosphonium ion to form a pentacoordinate intermediate (86) which undergoes the ring expansion to the phosphinine derivative (87) (Scheme 9). 

The triple bond of phosphaalkynes also acts as a dienophile with phosphole sulfides, giving a cycloadduct (167) that readily loses the bridging phosphine sulfide group and is converted to a phosphinine derivative, (168) (Scheme 34) <86ZN(B)93l>. The reaction has practical value as a phosphinine synthesis. 

Markl Nirenberg, Ochoa and Khorana Heterocyclic phosphinine derivatives first synthesised Elucidation of the Genetic Code (Nobel Prize 1968)... 

Published data on the properties and reactions of phosphinine is still somewhat limited. A few years earlier the first phosphinine derivative, 2,4,6 triphenylphosphinine was synthesised by Markl from pyrilium fluoroborate (6.861). Electron diffraction and crystal structure analyses have confirmed the presence of planar rings with equivalent P-C bond lengths in both these compounds (6.862). The intense UV spectra, ring-vibration frequencies and low-field NMR shifts of the ring protons are all consistent with 3pji-2pjr aromatic delocalisation in this class of compound. Addition readily occurs (6.863). 

SCHEME 16 The conversion of 3-phosphinoyl-phosphinine derivatives to cis-chelate Pt complexes. 

Ring-expansion reactions of phospholes by formal insertion of methylene fragments lead to 2-substituted phosphinines as described by Mathey et al. In this way, the first phosphinine derivative of 2,2 -bipyridine (NIPHOS, 5) was synthesized (Scheme 6.4) [27]. 

Fig. 6.11 Rh(I) complex containing a phosphinine derivative of 2,2 -bipyridine and the molecular structure of 24 in the crystal...

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