Alkenes Staudinger reaction

Two possible [2+2] cycloadditions can be envisaged for the synthesis of (3-lactams (Scheme 1). Interestingly, the same fragmentations have been observed in the mass spectra of these compounds [10, 11], One possibility consists of the [2+2] cycloaddition between ketenes (2) and imines (3) to yield (3-lactams (1). This reaction has been explored experimentally and it is also known as the Staudinger reaction between ketenes and imines [12-15]. In an alternative approach, the [2+2] cycloaddition between alkenes (5) and isocyanates (4) leads to (3-lactams (1). This reaction has been less extensively used, but it has proven to be useful in the chemical synthesis of interesting compounds [16-19]. 

A perfunctory study of the Staudinger reaction ( rich alkene + ketene — cyclobuta-none)49 can lead us to believe in a failure of FO theory. The alkene, being rich in electrons, will react preferentially by its HOMO and the ketene by its LUMO. Also, as nco is lower than jtcc, the cycloaddition should give a methylene oxetane and not a cyclobutanone. 

As in similar cycloadditions of ketenes and alkenes, the Staudinger reaction is likely to occur via dipolar intermediates 4 in a thermally allowed two-step process to give ds-3,4-disubstituted azetidin-2-ones 5 stereoselectively. 

Certain aldehydes and ketones, when used as solvents, intercept and reduce a labile intermediate in the ozonolysis of olefins. The intermediate, which can be considered the progenitor of many other ozonolysis products, is formulated as the Staudinger molozonide, e.g. (577), and its reduction generates the corresponding dioxetan (578) with a Baeyer-Villiger oxidation of the aldehyde or ketone solvent. The dioxetan intermediate, normally cleaved to the carbonyl components, has now been isolated and characterized by using pinacolone as a solvent. Low-temperature infrared studies of simple alkene-ozone reactions have been made. ... 

The mode of formation of the free radicals is rather unimportant for the present purpose since they may be considered to serve only to initiate the reaction. The free radical, R —, reacts with the alkene (e.g., CH2=CHR, where R may be hydrogen or alkyl) in the following manner (Staudinger, 8 Flory, 9 Price, 10) ... 

The Barton-Kellogg reaction is a coupling reaction between a diazo compound and a thioketone to give an episulfide. Desulfurization of the episulfide to alkene can be accomplished by phosphine or by copper powder. This reaction has been pioneered by Hermann Staudinger and therefore the reaction also goes by the name Staudinger-type diazo-thioketone coupling. 

These reactions, first described by Staudinger, have received little attention. A more recent investigation shows that the bond of the thiones regioselectively adds across the C =C bond of the ketenes (equation 11) to form 2-thietanones 0-thiolactones). Primaiy adducts have been isolated only in a few cases. Most often they spontaneously decompose to yield an alkene and COS (equation 12). 

The most important carbene reaction - mechanistically and for synthetic applications - is the cycloaddition to alkenes, i. e., the formation of cyclopropanes. This reaction was studied briefly by Buchner and Geronimus (1903) long before Hine s rediscovery of carbenes. They found ethyl 2-phenylcyclopropanecarboxylate in the reaction of ethyl diazoacetate with styrene. Besides the attention given by Staudinger et al. (1924), however, little attention was paid to that work, apart form the fact that it may be a 1,3-dipolar cycloaddition followed by an azo-extrusion (Sect. 6.5). 

The common methods for the S5mthesis of p-lactams are cycloaddition reactions such as the Staudinger s ketene-imine cycloadditions, ester enolate-imine cycloadditions, alkyne-nitrone cycloadditions (Kinugasa reaction), alkene-isocyanate cycloadditions, and Torii s cyclocarbonylation of allyl halides with imines. Several cyclizahon reactions of p-amino esters, p-amino acids, p-hydroxamate esters, and a-diazocarbonyls have been developed for the formation of p-lactam ring. N,N-Disubstituted a-haloamides cyclize by C3-C4 bond formation leading to the formation of P-lactam ring. 

---