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The reaction between tert-butylmagnesium chloride (or tert-pentylmagnesium chloride) and the particular phosphorus–sulfur bond of a benzothiadiphospholic system showed, for the first time, evidence of formation of intermediates with a four-center structure. The possibility, for the phosphorus atom, to have very stable hypervalent coordinations makes it possible to observe its hypervalent states during the course of a reaction. The benzothiadiphosphole, with its bicyclic folded structure, further stabilizes the hypervalent coordinations thus making the intermediates sufficiently stable to be detected during the course of the reaction by 31P NMR spectroscopy, which revealed the nature and the stability of the species involved in this reaction, carried out also using other Grignard reagents.

This letter describes a new one-pot method for the synthesis of unsymmetrical aryl methylphoshinates by insertion of phosphorus moiety into the OMe bond of anisoles. These products are very difficult to obtain with other reported methods requiring several steps.

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.

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.

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.

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.