P—C heterocycles

The sixth chapter, Preparation, Structure and Biological Property of Phosphorus Heterocycles with a C-P Ring System by Mitsuji Yamashita presents a very critical review of novel phosphorus heterocycles. The review discusses aliphatic 4-, 5-, 6- and 7-membered C-P-C heterocycles, aromatic C-P-C heterocycles, and various C-P-0 type heterocycles including phospha sugars. Synthetic aspects, structural studies, and the biological properties of these phosphorus heterocycles are also addressed. This chapter may attract the interest of synthetic chemists as well as heterocyclic and heteroatom chemists in the life science fields. 

Presumably, 9 is actually formed from carbene 8 in the pyrolysis zone by a P/C phenyl shift, but then apparently succumbs to fast transformation into the thermodynamically stable final products. Formation of the methane derivative 13 should be preceded by a 1,2-phenyl shift to give the shortlived 10, the production of fluorene (14) by the occurrence of diphenylcarbene (II), and the formation of benzophenone (15) by isomerization to the angle-strained three-membered heterocycle 12, which is followed by elimination of phenylphospbinidene. No direct evidence is available for the intermediacy of 10-12. 

A series of amine-reactive, long-wavelength fluorescent labels 48a-48c was recently developed on the basis of a norsquaraine chromophore [97, 98], Importantly, norsquaraine dyes show shifted pK3 values as compared to norcyanines with the same heterocyclic end-groups by several pH units e.g., while the unsymmetri-cal norsquaraine 48b has a p/C, around 11.2, the norcyanine dye 47d carrying the same substituents has a p/sTa of 7.5 [118]. Due to this pATa-shift to the alkaline pH range, some of these norsquaraines are also useful as fluorescent labels as their spectral properties are not affected in the pH range below 7.5. 

P=C moiety in heterophospholes undergoes cycloaddition reactions with a variety of dienes and dipoles to afford a range of new heterocycles having bridgehead phosphorus atom [2, 4, 97, 98]. Previously, the reactivity of diazaphospholes towards cycloaddition reactions has been investigated to a limited extent [98],... 

One of the possible synthetic ways to obtain heterocyclic phosphines is the insertion of carbonyl compounds into the P—E (E = Si, Ge) bond of sila- and germa-phospholanes. Thus, the enlargement of the ring takes place and the P—C—O—E fragment is formed (9) [Eq. (7)] (74MI1 75JOMC35 77JOM35). The heterocyclic phosphepanes are obtained as a mixture of stereoisomers. 

Intermolecular cyclization of allyloxycarbonylphosphines in the presence of azabisisobutyronitrile also results in the formation of heterocycles containing the P—C—O fragment (11) [Eq. (9)] (82ZN965). 

Heterocycles with the P—C—O fragment can be obtained by rearrangement of functionally substituted phosphines. For example, tris(hydroxyethyl)phosphine isomerizes into 5-methyl-5-oxo-1,3,5-dioxaphosphorinane (15) in the presence of formaldehyde [Eq. (13)] (78ZOB2653). 

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