The sex pheromone of the brownbanded cockroach, Supella longipalpa, can be synthesized by direct coupling of a brominated pyrone with an alkylzinc reagent. The stereochemistry of the natural pheromone has been assigned as (2′R, 4′R)-5-(2′,4′-dimethylheptanyl)-3-methyl-2H-pyran-2-one by a combination of synthesis, chiral gas chromatography, and electrophysiological measurement.
Conjugate addition-rearrangement of N-benzylhydroxy-lamine to lactone 6 provides isoxazolidin-5-one 7 which was in turn mesylated at the hydroxy group and subjected to the next skeleton rearrangement to afford 3,5-disubstituted isoxazolidine 10. Standard transformation of 10 gave negamycin lactone 4.
Enantiopure enones obtained via lipase asymmetrization of meso-diols derived from cycloheptatriene underwent tin-directed ring-openings to give syn-1,3-bis(silyloxy) olefins which were converted to their acetonides in a one-pot sequence.
Dialdehydes derived from digoxin glycosides via sodium periodate oxidation were regioselectively deglycosylated by various amino acids in anhydrous methanolic solution to afford excellent yields of digoxigenin bis-digitoxoside and digoxigenin mono-digitoxoside in a single step.
Eleven-membered dolabelladiene carbocycles have been transformed into several tricyclic ring systems via efficient, stereocontrolled, transannular olefin-enone cyclizations. Ring contractions of the [9.3.0]cyclotetradecane.nucleus have provided 5-7-6 dolastane and 5-8-5 fusicoccane carbocycles.
Thieno[2,3(3,2)-f] indolizines were synthesized from 2-formyl-1-[thien-2(3)-ylmethyl]pymole. Under Diels-Alder reaction with diethyl acetylenedicarboxylate they led to cycl[3,2,2]azines fused to a thiophene ring.
The enyne needed for coupling to a CD-ring fragment, namely, 3S, 5R-oct-1-en-7-yne-3,5-diol, in the Trost-Dumas carbopalladation route to 1α, 25-dihydroxyvitamin D 3 was synthesized from D-xylose in 13 steps and 21% yield.
Treatment of the acyl selenide 7 with triphenyltin hydride and triethylborane generates the acyl radical which undergoes 5-exo trigonal cyclization to afford the 2,5-disubstituted tetrahydrofuran-3-ones 10a/b in 97% yield as a 94:6 mixture of diastereoisomers.
α-Ketosulphides of benzothiazole 1 react with allylic carbonates in the presence of palladium acetate in dichloromethane under mild conditions affording α,α-diallylated ketosulphides 2 in high yields. Reduction of 2 with sodium borohydride in isopropanol gives episulphides which in turn can be transformed almost quantitatively into trienes.
Water-soluble hydroxocomplexes 2, easily formed from organotin trihalides 1 in aqueous alkaline solution, react readily with aryl halides in the same medium in the presence of palladium complexes to give cross-coupled products 3 in high yields.
We describe here a new type of fragmentation pathway leading to diquinane skeletons, where the normal reactivity of the systems is dramatically altered by a suitably positioned radical stabilizing groups.
The first total synthesis of clonostachydiol has been achieved from two appropriately protected hydroxy acids that are derived from (D)-xylose and 1,2-O-isopropylidene (D)-glyceraldehyde. This synthesis has proved the absolute configuration of four stereocenters in clonostachydiol as 2R,3S,8R,11R unambiguously.
The first highly asymmetric Pummerer-type cyclization of chiral, non-racemic β-amidosulfoxides leading to enantiomerically enriched β-lactams (80–85 % ee) is described. S-and R-sulfoxides (S-2a-d and R-2a-c) were treated with O-methyl-O-tert-butyldimethylsilyl ketene acetal (1) in the presence of a catalytic amount of ZnCl 2 in CH 2 Cl 2 to predominantly give the corresponding...
The readily available α,α'-phthalimidoyldibromide 2 has been converted to the first reported N-substitutedoxyallyl cation by treatment with either CF 3 CH 2 OH or 3M LiClO4Et2O in the presence of Et 3 N. The formation of this reactive intermediate has been demonstrated by its in situ cycloaddition with cyclopentadiene and furan.
On reaction with triflic anhydride, the hept-1-enitols resulting from the Wittig reaction of tetra-O-benzyl d-hexopyranoses with [Ph 3 PCH 2 ] lead, in one step, to 3,6-anhydro-hept-1-enitol derivatives (“C-vinyl furanosides”) in high yield, by way of the participation of the benzyloxy group at C-3 with concomitant debenzylation.
Excellent regiospecificity has been achieved in the reaction of carbon nucleophiles with N-para-toluenesulfonylaziridine-2-carboxylic acid (6, R = H protected as the anion. This has been developed into a general and high yielding synthesis of optically pure α-amino acids containing one chiral centre. When the aziridine (20) containing a second chiral centre was used, only lithium trimethylsilylacetylide...
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