Mohammed Ahmar

Carbopalladation of β-allenylmalonates : a way to cyclopentenyl or vinylcyclopropyl derivatives.

Abstract The palladium-catalyzed addition of a vinyl or aryl halide to the enolate of β-allenyl malonate 2 leads to the formation of either of the two cyclized products 3 and 4 depending mainly on the bulk of the starting unsaturated halide.

Glucosyloxymethylfurfural (GMF): a creative renewable scaffold towards bioinspired architectures

Abstract Glucosyloxymethylfurfural (GMF) is the glucosylated analogue of hydroxymethylfurfural (HMF), and is obtained in one step from the very available disaccharide isomaltulose. This account gives an overview on the preparation and the uses of GMF towards architectures containing a carbohydrate moiety and shows that rather elaborated targets can be synthesized from GMF in very short sequences. A special focus is made on carbon–carbon formation on the aldehyde group leading to new biobased acrylic derivatives by the Baylis–Hillman reaction.

Stereocontrol in organic synthesis using silicon-containing compounds. A synthesis of methyl (+)-nonactate

(3Z,2S)-7,7-Ethylenedioxyhex-3-en-2-yl N-phenylcarbamate 7 gave the allylsilane 8, (2E,4S)-7,7-ethylenedioxy-4-dimethyl(phenyl)silylhept-2-ene, introducing one stereogenic centre carrying a silyl group. Hydroboration–oxidation gave (2S,4S)-7,7-ethylenedioxy-4-dimethyl(phenyl)silylheptan-2-ol 9, controlling a second stereogenic centre. Conjugate addition of the phenyldimethylsilylcuprate reagent to the α,β-unsaturated imide (2′E,6′S,8′R,5S)-1-[8′-benzyloxy-6′-dimethyl(phenyl)silylnon-2′-enoyl]-5-triphenylmethoxymethylpyrrolidin-2-one 11 introduced a third stereogenic centre, and methylation of the ester derived from the product introduced a fourth. Ester hydrolysis and a double silyl-to-hydroxy conversion gave (2S,3S,6S,8R)-8-benzyloxy-3,6-dihydroxy-2-methylnonanoic acid 16, from which methyl (+)-nonactate 2 was prepared by differentiating the hydroxy groups with the selective formation of a β-lactone 17 rather than a seven-membered lactone.

Carbohydrate steroid hybrid architectures: the viewpoint of amphiphilicity and self-organisation

Carbohydrate steroid hybrids (steroid glycosides, glycosyl steroids and related compounds) are ubiquitous natural products, with immense structural diversity. They also show a common feature of being amphiphilic in character, which will be the major subject reviewed in this chapter. It will be preceded by an introduction on the occurrence and properties of glycosteroids, and their classification into three main sub-families based on their overall molecular shape and polarity where systems have: (i) one saccharidic part and one steroidal part, possibly including a spacer chain; (ii) saccharidic connections at two different points of the steroid, and (iii) an additional appendage that can be either polar or non-polar.

Epoxidation of 4-Alkylidenecyclopentenones

The exocyclic double bonds of 4-alkylidenecyclopentenones are selectively epoxidized by MCPBA to give epoxy-cyclopentenones, which under acidic conditions undergo ring-opening to furnish diols.

Selective monoalkylation of the fulvene-type enolates of 4-alkylidene- cyclopentenones

4-Alkylidenecyclopentenones were shown to be prone to polyalkylation because of their very easy enolization. They were selectively monoalkylated through the organozinc aided alkylation of their new fulvene-type enolates.