Schonberg reaction

The photochemistry of thiocarbonyl compounds has been extensively studied over the past three decades, and a variety of photochemical reactions are developed [1-8]. One of the earliest photochemical reactions of thiones is the reaction with oxygen [9]. Schonberg and Stephenson reported a detailed study of the photodimerization of thiophosgene and the wavelength-dependent pho-... 

Historically, the first reactions involving thiocarbonyl ylides involve the preparation of thiiranes and 1,3-dithiolanes from diazomethane and thiocarbonyl compounds reported early in the last century by Staudinger and co-workers (12,13). Similar reactions have been smdied by Schonberg and co-workers (14—16) during the 1960s, but neither was the reaction mechanism understood nor have thiocarbonyl ylides been recognized as key intermediates. [For some remarks to this subject see (8) and (10) in (17).]... 

Benzil undergoes a cycloaddition reaction with stilbene and 1,1-diphenyl-ethylene to form adducts containing the 2,3-dihydro-[l,4]-dioxin ring system and with visnagin to form an oxetane. These reactions and the cycloaddition reactions of the analogous o-quinones are reviewed by Schonberg.87... 

The reaction is named after Strecker,63 who reacted a-amino acids with alloxan, obtaining C02 and the purple murexide. The reaction was reviewed by Schonberg and Moubacher,64 its contribution to food flavour being covered by Rizzi.65... 

An interesting side reaction accompanies this synthesis leading to denitration or rearrangement of the nitro group.40 This behavior is again a feature of the (amino group and we have proposed the intermediacy of the hydrofuroxan (101) to account for it (cf. Schonberg... 

A52. A. Schonberg, G. O. Schenk, and O.-A. Neumuller, Preparative Organic Photochemistry, 2nd ed. Springer, Berlin, 1968. Chapter 45, pp. 459-470 Photochemical formation and reactions of organometallic compounds. 

For the preparation of hydrazones, Schonberg " recommends that equivalent amounts of the ketone and hydrazine be refluxed in -butanol (b.p. 117.7°) for 2 hrs. Use of ethanol requires a longer reflux period and use of ethylene or propylene glycol may lead to side reactions. Thus on applying the glycol procedure for conversion of fluorenone to the hydrazone, Baltzly et al. observed formation of considerable fluorene (interference by an unusually facile Wolff-Kishner reaction). On refluxing the reactants in n-butanol for 4 hrs., the hydrazone was obtained in 67% yield. However, a superior method for the preparation of hydrazones involves reaction of the ketone with N,N-dimethylhydrazine which see) followed by an exchange reaction with hydrazine. 

The same insertion of a methylene group between a benzene ring and carbonyl group is also found in the reaction of coumarandione (105- 106107).182 (The reaction course described by Schonberg... 

Schonberg and Frese987 report that reaction of ethyl diazoacetate or a diazo ketone with an aromatic thioketone in the presence of copper powder gives the / ,/ -disubstituted acrylic ester or the, / -unsaturated ketone, respectively, in 80-90% yield. 

Scheme 19.7 Chapman, Schonberg, and Newman-Kwart reactions.

---