Gabriel method

Wipf and Miller have reported side-chain oxidation of 3-hydroxy amides with the Dess-Martin periodinane, followed by immediate cyclodehydration with triphenylphosphine-iodine, which provides a versatile extension of the Robinson-Gabriel method to substituted oxazoles. Application of this method was used to prepare the oxazole fragment 10 in 55% overall yield from 3-hydroxy amide 8. 

Further examples, noted too late for inclusion in Table 2, are the preparation of 1- and 2-arylaziridines by the Wenkcr synthesis,[Pg.537]

Aniline cannot be prepared by the Gabriel method. Aryl halides do not undergo nucleophilic substitution under these conditions. 

Acylamino ketones also provide a convenient synthesis of thiazoles on treatment with phosphorus pentasulfide (Gabriels method). Substituents are usually restricted to alkyl, aryl, and alkoxy derivatives. Thus, the -acylamino ketone 234 with P4S10 gave the thiazole 240. Lawessons reagent (LR) can be effectively used as the source of sulfur in these cyclizations (e.g., Scheme 116) <1996JME957, 2006TL2361, CHEC-III(4.06.9.1.3)682>. 

Gabriel method based on the cyclization of 2-haloalkyl amines with a base. This method was used for the first commercial production of ethyleneimine. 

Diethylphosphoryl azide gives an Mo-triazoline with noibomene subsequent photolysis gives the phosphorylated aziridine, but pyrolysis gives the imine isomer. Maikovnikov addition of diethyl dibro-mophosphoramidate to alkenes (BF3 catalysis) occurs in high yield the initial adducts were converted to IV-unsubstituted products but would be readily convertible to phosphorylated aziridines ty the Gabriel method.In any case, IV-unsubstituted aziridines are readily phosphoiylated. > ... 

The Gabriel method of making primary amines (Scheme 2.33) rests on the fact that the imide hydrogen of phthalimide is rendered acidic by the two carbonyl groups. It therefore forms a potassium salt, which is a powerful nucleophile and may be alkylated. Hydrolysis of the amide generates the primary amine. The cleavage of the phthalimide may be carried out with hydrazine (H NNHj). 

The addition of amines to activated cyclopropanes with opening of the three-membered ring was also applied for the preparation of bicyclic systems with the nitrogen as bridgehead atom. These transformations involved the intramolecular nucleophilic attack of a primary amine which was generated by the Gabriel method. 

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