Hydantoins benzils

Benzilic acid rearrangement Benzoin reaction (condensation) Blanc chloromethylation reaction Bouveault-Blanc reduction Bucherer hydantoin synthesis Bucherer reaction Cannizzaro reaction Claisen aldoi condensation Claisen condensation Claisen-Schmidt reaction. Clemmensen reduction Darzens glycidic ester condensation Diazoamino-aminoazo rearrangement Dieckmann reaction Diels-Alder reaction Doebner reaction Erlenmeyer azlactone synthesis Fischer indole synthesis Fischer-Speior esterification Friedel-Crafts reaction... 

S-methylisothiourea (which is more correctly termed a substituted amidine) has already been mentioned above and elsewhere <8uoci30l>. Pyruvaldehyde reacts with ureas to form 4,5-dihydroxyimidazolin-2-ones which dehydrate to hydantoins <86JHCii25>, while benzil gives 4,5-diphenyl-4-imidazolin-2-ones ((241) R R = Ph) when heated with thioureas in acidic solution (Scheme 173) <9UCS(P2)1501>. Direct cyclocondensation of an a-bromoketone with urea forms around 50% of 2-imidazolinone when refluxed in ethylene glycol in the presence of an excess of... 

Disubstituted hydantoins and 2-thiohydantoins, especially their 5,5-diaryl derivatives, have been prepared by means of a condensation that involves a rearrangement similar to that in which benzilic acid is formed from benzil.1,3 Examples include the synthesis of fluorinated hydantoins,35 spirofluorene-,36 and spiroacenaphthylenehydantoins,37 2-thiohydantoins,30 38 39 and 5,5-diphenylhydantoin-2,4,5-13C3.40... 

Benzilic acid rearrangement Benzoin reaction (condensation) Blanc chloromethylation reaction Bouveault-Blanc reduction Bucherer hydantoin synthesis. Bucherer reaction. . ... 

Condensation of urea with carbonyl compounds A rapid and efficient MW-assisted synthesis of hydantoins and thiohydantoins was described by Muccioli et al. [117]. The most straightforward conditions for synthesis of phenytoin are the base-catalyzed condensation using benzil and urea, known as the Biltz synthesis (Eq. 33). MW activation of the Biltz synthesis of phenytoin improved both yield and reaction time. The first step consists in MW activation of the reaction of benzil with (thio)urea the second includes the conversion of the resulting 2-(thio)hydantoin to hydantoin using hydrogen peroxide. When reactions were performed at the same temperature under both reaction conditions, yields were by far better under the action of MW and emphasized the evident specific MW effects. These are perfectly expected when one considers the polar TS involved in the first step (nucleophilic addition of neutral NH2 group on carbonyl moiety). 

A rapid and efficient microwave-assisted synthesis of hydantoins and thiolydan-toins was reported by Muccioli et al. [74], The reaction is known as Biltz synthesis and is the base-catalysed condensation of benzil and urea. It was observed that microwave irradiation reduced the reaction time as well as increased the yield of the product as compared to the conventional method. The reason behind this is the involvement of polar transition state, i.e. nucleophilic addition of a neutral NH2 group to a carbonyl site (Scheme 11.21). The yield via the conventional method was 36 % when heated for 2 h whereas the yield via microwave irradiation was 80 % when heated only for 30 min. 

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