Phosphorus heterocycles, four-membered

Ylidic four Tr-electron four-member X -phosphorus heterocycles as electronic isomers of heterocyclobutadienes 98AG(E)270. 

The diazaphosphane or aminoiminophosphane ligands with a NPN framework are another subclass of cyclophosphazenes. These compounds with both phosphorus in oxidation state (111) [104-110] and (V) [111-112] have been employed in the synthesis of four membered heterocycles and coordination chemistry with group 13 derivatives. Several complexes of trivalent phosphorus derivatives with both aluminum halide and alkyls are known as illustrated for 48 in Scheme 21 [113-119]. The structure determination of 48 confirms the formation of a four membered metallacycle [116, 117],... 

Diathiadiphosphetane disulfides are probably the most studied and the most thermally and hydrolytically stable of all the phosphorus-chalcogen heterocycles. They contain a central four membered P2S2 ring and can be prepared from heating phosphorus pentasulfide with aromatic compounds. The most well-known of these is Lawesson s reagent (43), which is made from anisole and phosphorus pentasulfide,92 and is used extensively in organic synthesis procedures (see Section 5.4.1). Other dithiadiphosphetane disulfides of note are 44 and 45, formed from the reaction of phosphorus pentasulfide with ferrocene or 1 -bromonaphthalene respectively.93... 

Vacuum thermolysis (160°C) of the hemiaminal 11 generates the azaphos-phetane 65 in 85% yield.32 This product clearly results from the intramolecular insertion of the transient (amino) (phosphino)carbene 2h into the C-H bond of a diisopropylamino group bonded to phosphorus. Note that the four-membered heterocycle 65 is formed exclusively in spite of the ratio of six methyl-CH bonds to one methine-CH bond, and that only one of the two possible diastereomers is detected. The same regio- and diastereo-selectivity have already been observed with the di(phosphino)carbene 2g,74 but is in marked contrast to the exclusive formation of five-membered rings... 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

A fascinating feature of the chemistry of boron-phosphorus heterocycles is the existence of stable singlet biradicals, e.g. fBuBP Pr2)2 (for a discussion of the electronic structure, see Section 5.4.2.2). The synthesis of this four-membered ring is illustrated in Scheme 5.2. Related derivatives of the type (RBPR 2)2 are also prepared by a salt-elimination reaction of the appropriate lithium phosphide with a 1,2-dichlorodiborane or, in the case of the perphenylated derivative (PhBPPh2)2, by reduction of the cyclic dimer [Ph(Cl)BPPh2]2 with lithium naphthalenide (Scheme 9.11). ... 

Zwitterionic four-membered PN2Nb heterocycles were obtained in the reaction of ij5-phosphorus-nitrogen ylides with NbCl5 according to equation (40). 496... 

Phosphorinic, phospholanic, and phosphetanic acids are four-, five-, and six-membered phosphorus heterocycles, respectively, with a cyclic phosphinic... 

These reagents are usually prepared by treatment of a phosphine with an alkyl halide and successive addition of base, like BuLi or NaHMDS. Reaction with the ketone takes place by attack of the carbanionoid carbon of the ylide form on the electrophilic carbon of the carbonyl group via a four-membered heterocyclic transition state, the oxaphosphetane 35. The driving force for this transformation is provided by formation of the very strong phosphorus-oxygen bond. Subsequent collapse of the oxaphosphetane furnishes the desired exomethylene group under retention of geometry. 

Chapter 2 by Laszlo Nyulaszi and Zoltan Benko deals with the chemistry and physical organic chemistry of aromatic phosphorus heterocycles and is divided into four subchapters dealing with three-, four-, five-, and six-membered rings, in which there may be more than one phosphorus atom. The chapter begins with a clear presentation of the electronic structure that phosphorus may achieve in molecules with CP bonds. For cyclopentadiene and phosphole eight aromaticity indices are collected. Almost all of them indicate that phosphole is more aromatic than cyclopentadiene. It is also shown that even small structural effects (substituent, bonding modes) can have a substantial impact on the chemistry of the reported systems. 

The compounds with five-membered rings containing three or four heteroatoms including at least one phosphorus were first systematically reviewed in Chapter 4.22 of CHEC-II(1996) by Schmidpeter <1996CHEC-II(4)771>. In CHEC(1984), only few examples of 2//4,2,3-diazaphospholcs were mentioned in the general chapter on phosphorus heterocycles <1984CHEC(1)493>. 

The possibility of using phosphorus-containing heterocycles as ligands [496-499] represents an area of research of great interest. On the basis of these kinds of ligands, complexes of three-member saturated, for example 243 [497], and unsaturated 244 [498] heterocycles, as well as four-member heterocycles 245 [499] have been synthesized ... 

Initially, ring expansion by tellurium leads to a four-membered heterocycle (n = 1) intermolecular rearrangements produce additional tellurium-phosphorus hctcrocycles, which are ultimately converted by extrusion of tellurium to tetra-/-butylcyclotetra-phosphane1. 

A series of four-membered Si- or P-containing heterocycles was produced in various yields by electrocyclization or [2-t-2]-dimerization of compounds with multiple carbon-silicon or carbon-phosphorus bonds. These unsaturated species are formed under photolysis of diazo compounds containing a P or Si atom in an a position with respect to the diazo group, following a [l,2]-sigmatropic shift in the intermediate carbene. 

In conformity with the calculations the yicrz-fused heterocycles with a phosphorus atom proved to be quite stable. For instance, treating 1,8-dilithionaphthalene (18) with (A, A -diisopropylamino)dichlorophosphine afforded in a 75% yield a P-substituted naphtho[l,8-Z)c]phosphete (19) that took up tungsten pentacarbonyl to form a complex compound 20 (02AG(E)3897). The latter on further reaction with platinum tetratriphenylphosphinate and carbon monoxide suffers a recyclization of the four-membered ring into a five-membered one (20—>21). The reaction of... 

Four-membered heterocyclic systems have been postulated to be involved as intermediates along the reaction pathway in a number of systems allowing olefin synthesis. This is the case of the Wittig reaction (phosphorus) and a family of related reactions the boron-Wittig (boron), the Peterson (silicon) 44 and the Peterson-type reactions (germanium, tin, lead). 5,l46 11 these systems,... 

The study of the chemistry and biology of strained four-membered heterocycles has become an extremely active field of research in 2014. In this chapter, the reader will find a brief discussion of new contributions focused on fields such as organic synthesis and medicinal chemistry. For the sake of clarity, contributions are separated in sections depending on the nature of the heteroatom. Although oxa- and azaheterocycle derivatives dominate the field in terms of the number of scientific pubheations, the chemistry of sulfur-, silicon-, and phosphorus-based heterocycles is also of great relevance.The aim here is not to provide an in-depth analysis of all the vast scientific Hterature concerning four-membered heterocycles during the calendar year 2014. Consequently, there are many examples that are cited but not covered in detail. 

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