An improved synthesis of resveratrol

In this article we report an improved total synthesis of resveratrol, increasing the overall yield from 22 to 71%. The synthesis reported in our previous publication was made up of two fundamental steps: a Wittig reaction and a Heck coupling. Here we studied these steps separately to increase the individual yields. The yield of the Wittig reaction was increased up to 98%; however, we could not find better reaction conditions for the Heck coupling than those reported in the previous article.     

An improved synthesis of pennogenin

An improved synthesis of pennogenin, a bioactive component of Chinese herb “Chonglou” (Paris), is described. A ring-switching process opened the ring E of diosgenin and allowed the use of a hydroxyl-directed diboration/oxidation to introduce C17α-OH, hence eliminating the use of OsO₄. This strategy might be rendered to synthesize similar steroids with C17α-OH.     

An improved synthesis of isonitrosoacetanilides

A novel two-step synthesis of isonitrosoacetanilides [2-(hydroxyimino)-N-phenylacetamides] has been developed, involving the initial acylation of aniline derivatives with 2,2-diacetoxyacetyl chloride, followed by reaction with hydroxylamine hydrochloride. The method works equally well with a variety of different aniline derivatives, including those with poor aqueous solubility and those containing electron rich ortho-substituents, neither of which react well under traditional conditions.     

An improved synthesis of diiodonoradamantane

Τhe synthesis of 3,7-diiodo-tricyclo[3.3.1.0^3,7]nonane, the main precursor of noradamantene, by iodination of the corresponding diol via its dimesylate affords a threefold higher yield than the direct iodination of the diol. Neither the dimesylate nor the cyclic sulfate of the diol yields noradamantene upon reduction with sodium amalgam.     

An improved synthesis of tetramesitylporphyrin

We report a simple two-step one-flask procedure for the synthesis of tetramesitylporphyrin in 29% yield. Pyrrole and mesitaldehyde react at room temperature to form tetramesitylporphyrinogen. The addition of an oxidant yields the porphyrin. Macrocycle formation and oxidative aromatization are thus performed separately. The reaction at higher temperature results in a lower yield of porphyrin.     

An improved synthesis of norcocaine

An improved, high yielding procedure for the preparation of norcocaine from cocaine is described. The synthesis is accomplished by controlling the pH during the potassium permanganate oxidation. A quantitative conversion of N-benzoylecgonine methyl ester into norcocaine by dry, hydrogen chloride-dioxane is also included.     

An improved synthesis of galanthamine

Modifications in the total synthesis of the Amarylidaceae alkaloid of galanthamine from commercially available isovanillin and tyramine have resulted in a shortened reaction sequence, which is amenable to upscaling and in improved product yield.     

An improved synthesis of benzocycloalkanone derivatives

A convenient and improved annulation method for the synthesis of bicyclic ketones was developed. A 2,2-dimethyl-6-(2-phenylsulfonyl)ethylcyclohexanone was converted into a sulfonylester by the addition of ethyl acetate and subsequent dehydration. A Dieckmann type condensation of the sulfonylester followed by desulfonylation afforded the 8,8-dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalene-2-one in good yield. This annulation method was also applicable for the synthesis of the benzocyclooctanone derivative.     

An improved synthesis of 1-phenylpentafluoropropenes

1-Phenylpentafluoropropene and a number of its para- and ortho-substituted derivatives were prepared in high yields by reaction of hexafluoropropene with etheral solutions of corresponding phenylmagnesium bromides in sealed glass tubes under autogenous pressure. The products were obtained as mixtures of the Z and E isomers, which ratios varied from 1/2 to 1/6 in favour of the E forms. ¹⁹F n.m.r. and i.r. spectra and b.p. of the 1-phenylpentafluoropropenes are reported.     

An improved synthesis of rhinocerotinoic acid

The stereoselective synthesis of E-rhinocerotinoic acid has been achieved in five steps from (−)-sclareol in an overall yield of 32%. This constitutes a significant improvement on the previous synthesis of this anti-inflammatory compound.     

An improved synthesis of 3-aminoestrone

An efficient Pd(0)-catalyzed protocol for the rapid and efficient preparation of 3-aminoestrone via 3-benzylaminoestrone from estrone-triflate is described. The three step synthesis proceeds with an overall yield of about 55% using X-Phos as optimal ligand for the Pd(0)-catalyzed Buchwald-Hartwig amination.     

An improved synthesis of morpholino-glycoamino acids

The current synthesis of hybrid morpholino-glycoamino acids through double reductive amination is characterized by modest yields and lengthy reaction times. We propose an optimized procedure that results in improved yields and the shortest reaction times reported so far.     

An improved synthesis of 5,15-diaryloctaalkylporphyrins

The title compounds were prepared from an aromatic aldehyde and bis(3-ethyl-4-methyl-2-pyrrolyl)-methane in acetonitrile in the presence of catalytic amount of trichloroacetic acid, followed by p-chloranil oxidation. The reaction conditions employed here are milder than those previously reported, allowing efficient preparation of porphyrins with acid-labile groups such as cyclic acetals, for which the previous method provided no direct synthetic access. Using the new method, aromatic aldehydes with acid-labile groups, as well as sterically hindered aldehydes, gave the corresponding porphyrins in satisfactory yields (50–90%). This method therefore can be widely utilized for synthesis of 5,15-diaryloctaalkylporphyrins.     

An improved synthesis of 10-isobornylsultone

A modified and improved synthesis of 10-isobornylsultone in three steps and in 81% overall yield starting from (+)-camphor-10-sulfonic acid is described. The synthesis proceeds via methyl sulfonate ester formation, stereoselective reduction and base-catalysed intramolecular cyclisation.     

An improved synthesis of Fmoc-N-methyl-alpha-amino acids

A highly efficient and environmentally more benign synthesis of Fmoc-N-methyl-alpha-amino acids from the corresponding Fmoc-amino acid, via intermediate 5-oxazolidinones, has been developed by using Lewis acid catalysis for the reductive opening of the oxazolidinone ring.     

An improved synthesis of the scyphostatin side-chain

A formal synthesis of the lipophilic side-chain of scyphostatin has been achieved using a convergent synthesis, in 16% yield over six steps. This synthesis involves enzymatic desymmetrisation of a meso-diol, resolution of 2-methylbutan-1-ol, stereoselective hydrozirconation of a volatile acetylene and a Negishi-style cross coupling.