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.
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.
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.
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.
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.
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.
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 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.
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.
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.
N α -Boc-N α -methyl-N ω,ω′ -bis(benzyloxycarbonyl)-L-arginine and N α -Boc-N α -methyl-N δ -benzyloxycarbonyl-L-ornithine have been synthesized starting with Boc-L-Gln. The γ-carboxamide of Boc-L-Gln was dehydrated to a nitrile group and the resulting compound is selectively methylated providing N-Boc-2-methylamino-4-cyanobutyric acid. The nitrile is...
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.
Allyl isopropenyl dicarbonate (1) reacts with carboxylic acids in the presence of 4-dimethylaminopyridine(DMAP) catalyst to give allyl esters in high yields under mild conditions such as in a near-neutral medium at room temperature.
The reaction of phenethyliminophosphorane with arylketenes gave 1-benzyl-3,4-dihydroisoquinolines in good yields. An aza-Wittig type reaction of vinyliminophosphorane with p-toluenesulfonylisocyanate furnished 1-aminoisoquinoline 6 in high yield.
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.
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