No abstract

The structures and relative stereochemistries of rocaglamide, a novel antileukemic 1 H-cyclopenta [ b ] benzofuran isolated from Aglaia elliptifolia, and dehydrorocaglamide, derived from rocaglamide, have been established from spectral and single-crystal X-ray analysis.

Reported here for the first time is the iodobenzene-catalyzed alpha-oxidation of ketones, in which diacyloxy(phenyl)-lambda3-iodanes generated in situ act as real oxidants of ketones and m-chloroperbenzoic acid serves as a terminal oxidant. Oxidation of a ketone with m-chloroperbenzoic acid in acetic acid in the presence of a catalytic amount of iodobenzene, BF3.Et2O, and water at room temperature under argon affords an alpha-acetoxy ketone in good yield. p-Methyl- and p-chloroiodobenzene also serve as efficient catalysts in this direct oxidation. We found that when the reaction was carried out in the absence of a catalytic amount of iodobenzene, Baeyer-Villiger oxidation of a ketone took place. It is noted that use of water and BF3.Et2O is crucial to the success of this alpha-acetoxylation.

Scheme I 4 concomitantly, 2-methylene ketone 4g was formed (monitored by NMR). After 4 h, dehydrostannation was complete, and the precipitate was filtered off. Aqueous workup of the filtrate (pentane/aqueous NH4C1) followed by evaporation of the solvents and bulb-to-bulb distillation afforded 2-methylenecycloheptanone (4g) in 80% yield. Similarly, essentially quantitative conversion of 3 to 4 (eq 1) was observed in the reaction of 3 with Me2SO-d6/CDCl3 3 4 at 60 °C (by NMR) except for 3f which did not bear hydrogen ß to the stannyl group.9 The results are shown in Table I. The dehydrostannation of 3d,e,g,h proceeded with shorter reaction time than 3a-c. It seems that for dehydrostannation to occur, the intramolecular coordination of the carbonyl oxygen to the Sn atom (as indicated by IR) may play a key role. In fact, dehydrostannation did not take place with simple n-BuSnCl3 even under more forcing conditions (60 °C, 1 day). One plausible explanation for the present reaction is shown in Scheme I. The initial role of Me2SO may be the one as a base toward /3-hydrogen10 which may be sufficiently acidic due to the inductive effect of the adjacent carbonyl coordinated to the Sn. Thus, the deprotonation from 5 and subsequent destannylation via 6 would occur to lead to 4 and HSnCl3(Me2SO)" complex.11,12 Interestingly, the reaction of siloxycyclopropane 7 with SnCl4 in CH2C12 proceeded similarly and afforded ß-tríchlorostannyl aldehyde 8 (semisolid, vc=0 1680 cm-1). The (9) As the preparative method of /3-stannyl ketones 3, hydrostannation of ,/8-unsaturated ketones with HSnClg (in situ generated under acidic conditions: HC1 and SnCl2) has been known. The observed dehydrostannation promoted by Me2SO formally corresponds to its reverse reaction. See:

Large and small or twice moderate: Both combinations of trans influences of the substituents favor the formation of highly stable aryl λ3‐iodanes ArILL′ (examples: PhI(OH)OTs and PhI(OAc)2). trans influences also seem to explain why iodosylbenzene adopts an oxo‐bridged zigzag polymer structure in contrast to PhI(OH)2, which is monomeric.