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In this article, we present a study about the non-enzymatic hydrolysis of phosphoenolpyruvate (PEP) by following the reaction course through 31P NMR spectroscopy. We have demonstrated that PEP in water exists mainly as a very stable cyclic pentacoordinate phosphorus compound in equilibrium with other cyclic forms. This explains the PEP stability in water. In contrast, after addition of an alcohol to a PEP aqueous solution, other very unstable cyclic pentacoordinated intermediates are formed, which immediately collapse, giving a feasible phosphorylation of the alcohol. It is known that cyclic pentacoordinated phosphorus intermediates are favored over the corresponding acyclic intermediates by a factor of 106–108, and this preference, found also in this study, might be the “driver mechanism” able to overcome the clutter of abiotic chemistry, thus permitting formation of pre-RNA molecules probably with a “self-organized process.”

Asymmetric alkyl phospholanes have been diastereoselectively synthesized by addition of an unsymmetrical bis-Grignard reagent and of a mono-Grignard reagent to benzothiadiphosphole (1) and isolated as sulfides. The relative cis/trans ratio of the products depends on the steric hindrance of the mono-Grignard used. An accurate analysis of NMR and stereoselective data revealed the fundamental role played by hexacoordinated phosphorus intermediates in driving the stereochemical outcome of the reaction. The particular bicyclic and folded structure of reagent 1 strongly stabilizes hypercoordinated phosphorus species involved in the reaction and favors their formation. Pentacoordinate and metastable hexacoordinate phosphorus species have been detected and their evolution studied through (31)P NMR spectroscopy. The diastereoselective outcome of the reaction between reagent 1 and the couple bis-Grignard reagent 5/mono-Grignard reagent has been explained through a pathway involving hexacoordination of the phosphorus as a key step.

For understanding the mechanism involved in the Wittig reaction, it is important to know the factors which influence the stability of 1,2-oxaphosphetane intermediates with pentacoordinate phosphorus; in these intermediates, the steric factor plays a predominant role. Studying the Wittig reaction between nonstabilized ylides and different aldehydes, we noted that the stereochemical outcome driving toward Z-olefin formation was influenced only by different steric factors. The proposed mechanism differs from those previously reported because it underlines the fundamental role of the two cis/trans oxaphosphetane intermediates with the oxygen atom in equatorial position.

Fused 1,3-benzothiaphospholes 2 (cis-2,6,10-trimethyl-[1, 3]benzothiaphospholo[2,3-b][1, 3]benzothiaphosphole) reacts with H2O2 and S8, giving the corresponding oxide and sulfide, respectively. The reactions of 2 with diethyl azodicarboxylate (DEAD)/catechol or DEAD/o-aminophenol, o-azidophenol, and tetrachloro-o-benzoquinone (TOB) give the first examples of spiro pentacoordinated phosphorus derivatives of this heterocyclic system. The X-ray structural analysis of spiro compound 3 showed a trigonal bipyramidal configuration at phosphorus in which the three rings assume axial-equatorial positions.

The use of diazaphosphole derivatives generated in situ or the PCl3/hydrazone combination can be applied in a novel efficient one-pot procedure for the synthesis at room temperature of the title six-, seven- and eight-membered rings using always high concentration of the reagents (0.2–0.5M). N-alkenyl derivatives of 1,2-diazaheterocycles such as 8 (perhydro-pyridazine-3,6-diones), 9 (perhydro-1,2-diazepin-3,7-diones), 10 (perhydro-1,2-diazocin-3,8-diones) and 11 (1,2-dihydro-pyridazine-3,6-diones) were obtained by reaction of PCl3, ketone methylhydrazones and succinic, glutaric, adipic and maleic acids respectively. Changing the order of addition of reagents, or their simultaneous addition, gave identical results. In all the procedures the yields were good. The exclusive or prevalent formation of the E isomer was always observed. The E-configuration of the exocyclic double bond was deduced from some NOE experiments carried out on a E,Z mixture obtained by isomerization of the E isomer. Mechanism for the reaction is also proposed.

The use of a PCl3/hydrazone/dicarboxylic acid combination can be applied in an efficient one-pot procedure for the synthesis at room temperature of the title ring compounds that are also a new family of stable enamines. The phthalazinediones 7 were obtained in good yields by reaction of PCl3 with phthalic acid and hydrazones 1a,b,c containing hydrogen atoms only in one α position. Two structurally isomeric phthalazinediones (7 and 8) were obtained with hydrazones 1d,e,f,g containing hydrogen atoms in the two different α positions. When we used a methyl ketone hydrazone 1c,d,e,f,i, it was possible also to isolate the isomer containing an N-alkenyl group with two terminal hydrogen atoms. Where E,Z isomers are possible, the exclusive formation of the E isomer was always observed. As a rule, changing the order of addition of reagents gave almost identical results; however, in the case of phthalic acid, it is better to use the procedure in which PCl3 is added last to prevent the formation of the corresponding anhydride. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 291–296, 1999

The reaction of 1,2-diaza-1,3-butadienes with dialkyl phenylphosphonites under solvent-free conditions proceeds via zwitterionic intermediate and gives, by precipitation, the stable ylidic α-phosphanylidene-hydrazones that, in turn, can be transformed into the corresponding 3-phenyl-2 H -1,2,3λ 5 -diazaphospholes. The latter compounds are converted by hydrolytic cleavage in methanol–water (95:5) into E -hydrazonophosphonates that are useful for the preparation of the corresponding β-ketophosphonates and 4-[alkoxy(phenyl)phosphoryl]-1,2-diaza-1,3-butadienes. These peculiar 1,2-diaza-1,3-butadienes, bearing an alkoxy(phenyl)phosphoryl group on the carbon atom in position 4 are also able to add different nucleophiles, such as methanol or thiourea, giving 2-[alkoxy(phenyl)phosphoryl]-2-methoxyhydrazones and 5-phosphinate-substituted thiazol-4-ones, respectively.

The reaction under mild conditions of fused cis-1,2,3-benzothiadiphospholes (1) with RCOCl–AlCl3(R = Me, Et, Pri, CH2(CH2)2CH2Cl, hexyl, CH2Ph) gave fused cis-6-R-1,3-benzothiaphospholes (2)via a phosphorus carbon exchange, in good yields. Use of a variety of acyl chlorides showed that the reaction does not occur when the R group is very bulky. Following the reaction by g.l.c.–m.s., it was noted that, initially, trans-(2) is formed and this isomerizes to cis-(2). A mechanism for this unusual phosphorus–carbon exchange is reported.

We, the named authors, hereby wholly retract this Chemical Communication. Signed: Graziano Baccolini, Carla Boga and Gabriele Micheletti, Universita di Bologna, Italy, October 2011. Retraction endorsed by Dr Robert D. Eagling, Managing Editor. Retraction published 10 October, 2011.

The title compounds have been synthesized by a one-pot two-stage reaction of PCl3, ketone methyl-hydrazones and methyl acetoacetate. Both stages were carried out at room temperature and the corresponding 2-alkenyl-1,5-dimethylpyrazol-3(2H)-ones 5, which are an unknown series of pyrazolones, were obtained in good yields. Use of a variety of enolizable ketones has shown that the reaction always occurs with the predominance of the (E)-isomer. X-Ray structure determinations of an (E)- and a (Z)-derivative [(E)-5c·HCl and (Z)-5b] permitted the assignment of their structures. The aromaticity of these derivatives is discussed.

The one-pot reaction of the phenyldichlorophosphine-phenylazostilbene adduct with ortho-aminophenol led easily to the almost exclusive stereoselective formation of the cis-benzoxazaspirophosphorane. On the contrary, from the reaction with catechol the corresponding trans-spirophosphorane was surprisingly obtained.

The indolization of deoxybenzoin o , m , p (Me, MeO, Cl), p -NO2 and m -EtO-phenylhydrazones (1) by the above reaction has been examined. All the reactions are carried out at room temperature and high yields of the corresponding indoles (2) are obtained even when -NO2 substituent is present. In this case longer reaction time is necessary. Alkoxyphenylhydrazones give the corresponding indoles (2) in high yields without showing collateral reactions which indeed are present in several Fischer routes on these derivatives. m -Substituted phenylhydrazones (1) give a mixture of 4- and 6-substituted indoles in which the 6-isomer is always prevalent, a feature not inherent in the Fischer reactions. The regioselectivity is enhanced by the substituent steric hindrance increasing. The reaction can be also carried out at 0°C with a further improvement of its regioselectivity.

Stable spirocyclic phosphoranes 2 have been prepared stereospecifically in high yields (90–95%) by reaction of o-azidophenol with cis and trans-diazaphosphole derivatives 1. Slow isomerization of pure diastereoisomer 2 was observed in acidic conditions.

Thermal substitution reactions of M(CO)5Br (M=Mn, Re) with cis (L c ) and trans (L t ) diazaphosphole ligands (L=3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole) have been studied. It has been found that L c behaves as generally found for bulky phosphines affording to cis-M(CO)4(Lc)Br, mer-M(CO)3(L c )2Br and fac-Re(CO)3(L c )2Br which has been thermally isomerized to mer-Re(CO)3(L c )2Br. In contrast the corresponding reaction with the bulkier trans diazaphosphole isomer L t have only afforded cis-M(CO)4(L t )Br and mer-M(CO)3(L t )2Br. All the different stereochemical results are rationalized on the basis of the size of the central metals and of the steric demand of the ligands. The nature of the complexes has been established essentially by IR spectra which, in the case of cis-Re(CO)4(L c )Br presents in cyclohexane solution a doubling of all the characteristic v(CO) bands expected for the C 2v local symmetry. This unexpected result has been tentatively discussed also on the light of a...

Anisoles 4 react with AlCl3 and PCl3 to yield the new fused bicyclic system derivatives 5 and 6 as major products in a one-pot procedure. An alternative multi-step synthesis of this system is also reported in which bis(o-methoxyaryl)phosphane oxides 11 are treated with AlCl3 and PCl3; the diarylphosphane oxides 11 are obtained by a new simple method.

Reaction of diphenylnitrilimine (6) with phosphites (7) leads to the formation of α-phenylhydrazonophosphonates (9), whose configurational assignment about the CN bond has been determined.αβ-Bis(phenylhydrazono)phosphine oxide (10I)[or (10II)] is obtained by the reaction of (6) with diazaphospholen cis-(8)[or trans-(8)], a mixture of (10I and III)[or (10II and IV)] being formed only after work-up. Configurational assignments about the two CN bond have been determined and the relative configuration of the two chiral centres in (10I–IV) has been tentatively assigned. The stereospecificity of this reaction is explained in terms of spirocyclic pentaco-ordinate phosphorus intermediates whose formation may be favoured by ligand subset symmetry.

Thermal substitution reactions of [M(CO)5L1c] with cis diazaphosphole derivatives (L1= 3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole, L1c and L1t denote cis and trans L1 respectively) have yielded a mixture of cis and trans(2 : 3 ratio) tetracarbonyl complexes in which the ligands are bonded through the phosphorus atom. In contrast the reactions of [M(CO)5L1t] with the bulkier trans diazaphosphole isomers (L1t or L2t, L2= 5-benzyl-3,4-dihydro-2,3,4-triphenyl-2H-1,2,3-diazaphosphole) have only afforded the trans disubstituted tetracarbonyl [M(CO)4(Lt)2]. On the other hand, L1t and L2t have reacted with [M(CO)5L1c] affording the mixed-phosphine derivatives trans-[M(CO)4L1cLt](Lt= L1t or L2t). The norbornadiene complex [Mo(CO)4(nbd)] produced only cis-[Mo(CO)4(L1c)2] when treated with L1c in cyclohexane at room temperature, whereas with L1t no tetracarbonyl complexes (cis or trans) have been observed. In addition it has been found that cis(or trans)-[Mo(CO)4(L1c)2] thermally interconverts by a dissociative pathway to the trans(or cis)-[Mo(CO)4-(L1c)2] to give an equilibrium composition (cis : trans= 2 : 3) whereas trans-[Mo(CO)4(Lt)2] did not isomerize. All these different stereochemical results are tentatively explained by invoking fluxional or rigid five-co-ordinate intermediates in which only steric factors play a decisive role in determining the geometry and then the products distribution. The nature of the complexes has been established essentially by i.r. and 1H n.m.r. spectra. An X-ray study on cis-[Mo(CO)4(L1c)2] is also reported.

The reaction of thioanisole with PCl3 and AlCl3 leads to the title compound; its structural characterization is based on spectroscopic studies and confirmed by a single crystal X-ray diffraction of its dimethyl derivative.

Reaction of cis-[ReBr(CO)4( Lc)] with chiral Lc(cis-3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole) afforded fac-[ReBr(CO)3(Lc)2] which, owing to the racemic nature of Lc(R,S-L), should be a mixture of three predictable diastereoisomers: fac-[ReBr(CO)3(R-L)(S-L)][meso-(A) or meso-(B)] and the enantiomeric pair fac-[ ReBr(CO)3(R,S-L)2]. Two of these forms, meso-(A) and the enantiomeric pair, have been separated by column chromatography and their nature unambiguously attributed by X-ray studies. fac-[ReBr(CO)3(R-L)(S-L)] crystallizes in the monoclinic space group P21/n, with a= 19.481(4), b= 13.204(3), c= 20.083(8)A, β= 110.56(3)°, and Z= 4; R′= 0.046. fac-[ReBr(CO)3(R,S-L)2]·C6H14·C7H16 crystallizes in the monoclinic space group P21/n, with a= 12.191(3), b= 20.939(4), c= 21.713(5)A, β= 93.93(3)°, and Z= 4; R′= 0.048. Attempts to separate or detect spectroscopically isomers of fac-[ReBr( CO)3( L)2](L = racemic PMeEtPh) failed, indicating that interligand interactions are the determining factors in achieving the separation.

C(1) protonation of 4-alkyl-2-methoxy-1,4-dihydronaphthalene-1-nitronate anions (7) gives a mixture of trans-(9) and cis-4-alkyl-2-methoxy-1-nitro-1,4-dihydronaphthalenes (8) with the latter isomer in excess. Isomerization experiments indicate that the cis compound is also the more stable isomer. Formation of the more stable isomer under kinetically controlled conditions confirms that the stereochemistry of the reaction is governed by the steric hindrance offered by the axial alkyl group to proton attack in the axial direction in a transition state whose geometry reflects a boat conformation for (7).