Effect of steric bulk on the absolute reactivity of allene oxides.
Alpha-alkyl substituted fluorenylidene allene oxides were generated photochemically from appropriately substituted fluorenol derivatives in 2,2,2-trifluoroethanol (TFE) in order to assess the affect of steric bulk on the absolute reactivity of the allene oxides. The absolute reactivities of the allene oxides were measured using nanosecond laser flash photolysis, and were found to change little in TFE upon going from alpha-methyl to alpha-butyl to alpha-t-butyl. However, all three alpha-alkyl substituted allene oxides were considerably more reactive than the alpha-hydrogen derivative, indicating that steric bulk did not result in a decrease in reactivity as is typically found in other allene oxides. The contrary reactivity of the fluorenylidene allene oxides is explained by examining in detail the reactions of these allene oxides, determined from product studies.
An efficient cyclopentenone formation via an allene oxide
A new and efficient cyclopentenone annulation reaction has been developed. The annulation involves the in situ epoxidation [tBuOOH, VO(acac)2] of vinyl allenes 1a-f to furnish cyclopentenones 2a-f in 40~70% yield. This reaction closely resembles the proposed biosynthetic route to prostanoids.
Clozapine derived 2,3-dihydro-1H-1,4- and 1,5-benzodiazepines with D4 receptor selectivity: synthesis and biological testing.
Novel 4-arylpiperazin-1-yl-substituted 2,3-dihydro-1H-1,4- and 1H-1,5-benzodiazepines and their aza-analogues were synthesized as debenzoclozapine derivatives for evaluation as potential D4-ligands. While Ki values of some of the title compounds came within the range of clozapine, they showed an impressively greater selectivity over other dopamine receptor subtypes, especially D2. For the most promising compounds, intrinsic activity and binding properties to serotonin 5-HT1A and 5-HT2 were also determined.