Reaktive EC (pp) π-Systeme

Trifluoroselenomethionine: A New Unnatural Amino Acid

“…A solution of NaOMe (0.37 mmol) in methanol (2 mL) was added, and the reaction mixture was allowed to warm to room temperature. Analysis of the product by GC‐MS showed a molecular ion at m/z 196 and fragment ions at m/z 115 and 95, corresponding to the mass spectrum reported for the F 2 C=Se ( 10 )/cyclopentadiene Diels–Alder reaction product 3,3‐difluoro‐2‐selenabicyclo[2.2.1]hept‐5‐ene ( 19 , Scheme ) …”

“…When 18 was treated with sodium methoxide, with the reaction monitored by 19 F NMR, the only 19 F signal seen corresponded to fluoride ion, as confirmed by NMR analysis of a standard. When 18 was treated with sodium methoxide in the presence of excess cyclopentadiene at low temperature and the mixture was then slowly warmed, 3,3‐difluoro‐2‐selenabicyclo[2.2.1]hept‐5‐ene ( 19 )—the known cyclopentadiene adduct of F 2 C=Se—was detected by GC‐MS. Hence, decomposition of 8 upon heating in solution follows the path seen …”

The chemistry of fluorine containing phosphaalkenes, arsaalkenes and selenocarbonyls

“…Its preparation in quantitative yield and excellent purity enabled the investigation of the dienophilic properties in reactions with excess of acyclic and cyclic 1,3-dienes at low temperatures by warming up the adduct mixture from À196 to 25 8C. Reaction times between 4 and 15 s and 67-98% yields of the expected Diels-Alder adducts were observed (Scheme 18) [76]. The reactivity of the 1,3-dienes investigated decreases in the series: cyclopentadiene > 2,3-dimethylbutadiene, isoprene > pentamethylcyclopentadiene > 1,3-cyclohexadiene.…”

CaCl2-Promoted Dehydroxytrifluoromethylselenolation of Alcohols with [Me4N][SeCF3]

“… These reactions took full advantage of the equilibria between – XCF 3 (X = S, O) anions and XCF 2 with fluoride ions to produce trifluoromethyl (thio)­ethers. Nevertheless, as a comparison, the known MSeCF 3 complexes (M = SnMe 3 , 1/3B, 1/2Hg) decomposed to form carbonoselenoic difluoride (SeCF 2 ) under very harsh conditions . The decay of MSeCF 3 was slower and had a smaller tendency than that of the homologous – OCF 3 and – SCF 3 anions to OCF 2 and SCF 2 , respectively, , according to the calculated free energies of the similar conversions .…”

“…Nevertheless, as a comparison, the known MSeCF 3 complexes (M = SnMe 3 , 1/3B, 1/2Hg) decomposed to form carbonoselenoic difluoride (SeCF 2 ) under very harsh conditions . The decay of MSeCF 3 was slower and had a smaller tendency than that of the homologous – OCF 3 and – SCF 3 anions to OCF 2 and SCF 2 , respectively, , according to the calculated free energies of the similar conversions . More seriously, the SeCF 2 species was very easy to polymerize upon its formation under the reaction conditions .…”