Other Hydrogen Transfer

2 Other Hydrogen Transfers - Weigel and Wagner S have studied the 1,4-hydrogen abstraction reactions within the ketones (37) leading to the cyclopropanols (38). The study used wavelengths 300 nm with benzene or methanol as the solvents. The yields of products are shown below the structures. Polar solvents appeared to have no effect on the outcome of the reaction. 

6-hydrogen transfer is observed on irradiation of aldehyde (39). The resultant 1,5-biradical ring closes to afford the bridged compound (40) in 59% yield. The conditions which give the best results involve benzene solutions and quartz-filtered light.Kim and Park have reported that the photochemical cyclization of the benzophenone derivatives (41) results in the formation of dihydrobenzofurans (42). The most interesting result from this study is that there appears to be a dependence of the cis. trans ratio of the products on the substituent R. Thus when R is methyl the cis. trans ratio is 11 1 but when R is 

2 Other Hydrogen Transfers - Irradiation (A, 300 nm) of the ketoamines (31) in methanol solution results in the formation of the cyclopropanols (32) via the triplet excited state of the arylketo function. The reactions involve 1,4-hydrogen transfer processes and the yields range from modest to good. The 

The keto ester (42) undergoes photochemical hydrogen abstraction reactions to afford a 1,8-biradical.Again, in this case, the regiochemistry is controlled by the presence of the hetero atom. The resultant biradical cyclizes to yield the azalactone (43), the structure of which was determined by X-ray crystallography. The cyclization process is not stereoselective. 

2 Other Hydrogen Transfers Weigel and Wagner have studied the 1,4- 

Sauer et al have reported the photochemical reactivity of some dipeptides. To exemplify the reactivity of such systems the dipeptide (68) has been chosen. This, on irradiation, undergoes conversipn into the products (69) and (70) in the ratios shown. The reaction involves a 1,6-hydrogen abstraction and rotation within the resultant 1,5-biradical is hindered. Temperature effects 

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Ru(II), Ru(I) and Ir(I) in an aqueous medium (90). Data for the different complexes are shown in Table II. The highest conversion is observed with the ruthenium(II) complexes, which correlates with the facility of Ru complexes to catalyze other hydrogen transfer reactions. The complex PdCl2(TPPMS)2 has been used as a two-phase aqueous-organic catalyst for the carbonylation of allylic chlorides (Eq. 30) 91). The reaction pro-... 

While hydrogenation using metal hydrides and other hydrogen transfer reagents offers a feasible method for laboratory experimentations, activation of molecular hydrogen with metal or metal organic catalysts is broadly employed in industrial hydrogenation processes. 

Other hydrogen transfer reactions of glycine derivatives have been used to introduce functional groups at the a-position. For example, reactions with bromine or A -bromosuccinimide, fert-butyl perbenzoate in the presence of a copper catalyst, and tert-butyl hydroperoxide and formate, have been used to produce a-bromo-, benzoyloxy- and carboxy-substituted glycine derivatives, respectively (Scheme 2) [12-14]. 

The reactions described above involve the more usual 1,5-hydrogen transfer. However, other hydrogen transfer pathways can become available in suitably designed systems. Thus Roth et al have reported the cyclization of the amino-ketones (109) into the aminocyclopropanols (110) by a 0- or 1,4-hydrogen transfer pathway. 8- or 1,6-Hydrogen abstraction has been reported to arise from the /m -triplet state of some jS-aminovinyl ketones, e.g. (111).7 The reaction affords the pyrroles (112) in low to moderate yields by two sequential photochemical steps. Thus initial excitation produces the biradical (113), which ring-... 

Other Hydrogen Transfers. - A full account of the photochemical reaction of ketones with leaving groups adjacent to the carbonyl function has been published. This study provides a route to a variety of di- and tri-substituted cyclopropyl ketones. Caleulations have been carried out on the photobehaviour of oc-substituted butyrophenones to establish a mechanism whereby cyelopro-pane systems ean be formed.The photochemical behaviour inducing a hydrogen transfer reaction of 2-(6>-tolyl)benzofuran-3-one has been studied. ... 

Other Hydrogen-Transfer Reagents Group III Hydride-Donor Reagents... 

For other hydrogen-transfer reactions, satisfactory ab initio potential energy surfaces [115, 116] and approximate quantum trajectory calculations of isotope effects [136] are also available in a few instances, but for the most part experimental measurements have been compared with values calculated on the basis of empirical or semi-empirical potential surfaces, making use of transition-state theory, and discussion has centred on the pros and cons of the surface used and the type of tunnelling correction made [3, 19]. 

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