Graziano Baccolini

Substituent influence on the indolization with pcl3 of some o,m,p-substituted phenylhydrazones

Abstract 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.

Benzothiadiphosphole as phosphorus donating reagent for a new route to 2H-1,2,3-diazaphosphole derivatives

Conjugated azoalkenes 2 react at reflux toluene with fused benzothiadiphosphole 1 (or 4) to give the diazaphosphole 3 in 25–52% yields. With this route it is possible to isolate the so far unknown 3a which is difficult to obtain in other reported conditions. The P atom involved in this cycloaddition is the one between the two S atoms.

Role of phosphorus adducts in the indolization reaction between arylhydrazones and phosphorus trichloride

Abstract The reaction between arylhydrazones and PCl3 can give both diazaphospholes and indoles, via a common hypothetical diazaphospholine intermediate. The product ratio depends on the reaction conditions. In particular when a solvent which dissolves the phosphorus adducts is employed, indole is the almost exclusive reaction product. A mechanism is suggested for the whole indolization reaction. It Involves an acid promoted cleavage of the P-N bond of the diazaphospholine to give intermediates similar to those of the accepted Fischer indolization mechanism, where the dichlorophosphino group, substituting a hydrogen atom should have an important role in promoting of the loss of the amino group in the last stage of the reaction, via a “Wittig-like” elimination of Cl2PNH2.

An improved synthesis of fused 1,2,3-benzothiadiphospholes and a proposed reaction pathway

A fresh look has been taken at the reaction of PCl3 with thioanisole 1b and AlCl3 that gives, after treatment with water, the title compounds cis-2b in 38% yield together with small amounts of the isomeric cis-3b (2%). The course of this reaction has been studied by 31P-NMR spectroscopy. A multistep pathway, governed by the formation of several AlCl3 complexes with sulfur and phosphorus containing intermediates, has been proposed. The crucial step of this reaction is very reasonably an intramolecular electrocyclic ring closure of a diphosphane intermediate. From this plausible mechanism, an improved procedure that gives only the cis-2b isomer in 42% yield has been realized. In addition, an alternative synthesis using p-thiocresol that gives compounds cis-2b and cis-3b in a ratio of about 2:1 has been effected.

The role played by phosphorus hexacoordination in driving the stereochemical outcome of a phosphination reaction.

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.

One-Pot Synthesis of 1-Alkenyl Derivatives of Phospholane and Phosphinane − New Classes of Compounds

The synthesis of the title compounds at room temperature in a one-pot reaction involves the transfer of a phosphorus atom from a benzothiadiphosphole to incoming nucleophilic bis- and mono-Grignard reagents.

NEW 2H-1,2,3-DIAZAPHOSPHOLE DERIVATIVES AND RELATED RING-OPENED COMPOUNDS

Abstract The addition of phosphites to the azoalkene 1 gives mixtures of diazaphosphole derivatives 4 and related ring-opened compounds 3 in different proportions depending on the phosphite used. The compounds 3 have the Z-configuration, while cyclic compounds 4 are a mixture of isomers in which predominates the isomer bearing the C4-Ph and OR groups in a trans configuration. When P(OPh)3 is used in dry hexane with rigorous exclusion of moisture the new diazaphosphole derivative 5 is obtained. The results are explained in terms of the relative apicophilicities in the pentacoordinated intermediates.

An efficient procedure for the synthesis of N-alkenyl derivatives of six-membered and larger 1,2-diaza heterocycles

Abstract 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.

N-ALKENYL-3,5-PYRAZOLIDINEDIONES FROM KETONE HYDRAZONES, PCL3 AND MALONIC ACID

Abstract The title compounds 3 , a new series of 3,5-pyrazolidinediones, have been synthesized at room temperature by a one-pot reaction between ketone hydrazone 1, PCl 3 and malonic acid. Changing the order of addition of reagents, or their simultaneous addition, gave identical results. In all the procedures the yields are good and in the cases a,b,c and g the E -alkenyl isomer was obtained as the exclusive isomer. A dual mechanism which depends on the order of addition of the reactants is hypothesised.

A green synthesis of glycoluril derivatives in aqueous solution with recycle of the waste

Abstract A series of glycoluril derivatives have been synthesized in water at room temperature from urea and 1,2-dicarbonyl compounds in the presence of phosphoric anhydride. The reaction time is about 10 minutes using one mole of 1,2-dicarbonyl compound, three moles of urea, and half mole of P4O10, but the reaction occurs also, even if with longer reaction times, with very small amounts of P4O10 which is recovered at the end of reactions. In fact, several catalytic turnovers can be performed using the same reaction solution obtained after separation by simple filtration of the glycolurils.