Carbon heteroatom-enriched

Very recently, deprotonation-electrophile trapping of simple meso-epoxides was applied to medium-sized meso-cycloalkene oxides [77]. When cyclooctene oxide 62 is treated with s-BuLi in the presence of a diamine at -90°C, the Hthiated epoxide is stable enough to be trapped with a wide range of electrophiles, allowing the creation of carbon-heteroatom or carbon-carbon bonds [Eq. (33)]. The deprotonation is a symmetry-breaking step, and enantioselective deprotonation was successfully achieved in the presence of (-)-sparteine, leading to a range of enantio enriched functionalised epoxides 115 (in up to 86% ee). 

Pulse radiolysis shows that the pyrimidine radical cations are fairly strong acids and rapidly deprotonate at a heteroatom [reaction (98)]. As protonation/deprotonation reactions at heteroatoms are easily reversible, the radical cations are regenerated upon reprotonation. Deprotonation at carbon or reaction with water yields the final free-radical products [reactions (99) - (101)]. It is noted that in thymidine [23] and 5 -thymidylic acid [104] the allylic thymine radical is observed by EPR and there is very little question that its precursor is the thymine radical cation. The identification of the C(6)-OH-5-yl radical by EPR supports the view [100] that reaction with water competes with the deprotonation at methyl. Due to the ready oxidation of the (reducing) C(5)-OH-6-yl by peroxodisulfate, this type of radical is only observed at low peroxodisulfate concentrations in these systems, i.e. the (oxidizing) C(6)-OH-5-yl radicals are correspondingly enriched under conditions favourable to a chain reaction [22]. In the case of 1,3-dimethyluracil the interesting characteristics of... 

Urdahl et al. studied crude oils and silica-absorbed compounds (asphaltenes and resins) using C-NMR techniques (65). It was found that the asphaltenes and resins were enriched in condensed aromatics compared to the whole crude oils. There were strong indications of a long straight-chain aliphatic compound containing a heteroatom substituent which is abundant in paraf-finic oils. There was also reason to believe that this compound was active in the formation of stable water-in-crude oil emulsions. The range from 130 to 210 ppm in the NMR spectra was particularly of interest. This region represents quaternary aromatic and heteroatom-bonded carbons. 

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