Beilstein J. Org. Chem.2007,3, No. 47, doi:10.1186/1860-5397-3-47
. Fortunately, such an increase of reaction temperature enhances route c much more than route b.
For planar radicals, Rüchardt and Beckwith established that the C-H bond dissociation energy (BDE) for H-CXYZ compounds displays a good linear correlation with the measured α and β-proton ESR hyperfine splitting
constants. [17][18][19] When Y = Me, Z = H, the H-C BDE follows the order for X: CH=CH2 < Ph < PhCO = MeCO < CN < CO2Et < Me (Table 3, entries 1–7). The BDE for compounds where Y = Z = H follows the same order, albeit the value is of course slightly higher when compared to their methylated counterparts
presence of Et3B.
Addition of xanthate 1a to decene at r.t., catalysed by Et3B/air
Et3B/air catalysed intermolecular radical additions to olefins
Selected values of H-C BDE for compounds H-CXYZ from references [17][18][19].
Supporting Information
Supporting Information File 117: General procedure for
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Graphical Abstract
Scheme 1:
Reactivity of 2-oxoalkylxanthates toward 1-decene in the presence of Et3B/O2: competition between a...
Beilstein J. Org. Chem.2007,3, No. 46, doi:10.1186/1860-5397-3-46
found. A more seemly hypothesis is a hydrogen abstraction from the α-position of the boron atom. This reaction is well documented and energetically acceptable (BDE (C-H) = 80 ± 3 kcal/mol). For example, the methyl radical abstracts α-boronyl hydrogen of Et3B 124 times faster than hydrogen in the methyl
role of water or alcohols and solvents in the reduction of S-alkylxanthates and related compounds. Hydrogen transfer from the O-H bond present in water or in an alcohol is not an obvious hypothesis in radical chemistry because of the high BDE of the O-H bond. Our results corroborate Wood's findings
a complexation would lower the BDE of the O-H bond by 30 kcal/mol when compared to free H2O, thus rendering hydrogen abstraction from water a plausible process. The second route implies hydrogen abstraction from •O-O-H radical (O-H BDE 47.6 kcal/mol). The latter could possibly be formed by
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Graphical Abstract
Figure 1:
Xanthates 1a, 2a and their corresponding alkanes.