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A new family of analogs of steganacin, an important antimitotic compound, was accessed. It takes advantage of a completely stereoselective sequence of two key steps. The central dihydropyrane core is built by a highly diastereoselective and facially controlled hetero-Diels–Alder reaction. It is followed by a nonphenolic biaryl oxidative coupling with a complete atropo-stereoselectivity. It leads to a quick way to form cyclic biaryl lignans.

A high-yielding, practical two-step procedure for the preparation of N-benzylhydroxylamine starting from dibenzylamine is described. As specified in the detailed protocol, the reaction can be conveniently carried out on a > 0.5 mol laboratory scale.

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Efficient access to masked β-amino-aldehydes was performed starting from 6-alcoxy tetrahydrooxazinone 6a–d (6-ATO). Transacetalization leads to the opening of the cycle to form either unsymmetric acetal 7 or symmetric acetals 16–18. These amino acetals are key compounds, obtained with 99% ee, which can be engaged in efficient peptide coupling. This method could easily provide peptides aldehydes or small amido aldehydes as exemplified with the formal synthesis of ent-Maraviroc.

1,3-dipolar cycloadditions (1,3-DC) reactions involving nitrones as dipole have met a recent growing interest 1 – 8 especially in their diastereoselective and enantioselective versions. 9 - 10 This...

The reaction between octadecyl 3-(3,5-di- tert -4-hydroxyphenyl)propanoate and dibasic lead stearate, two compounds added in most PVC formulations, has been investigated in bulk. The structure of the resulting product, obtained after a one-pot synthesis, was characterized by HRMS and 2D NMR analyses. The product of empirical formula C 70 H 116 O 7 has been identified as an unknown highly substituted furan. The reaction mechanism between both products to produce this original furan has been established. The first step leads to a discoloured lead IV complex with bis-quinonemethide. The second step consist of a hydrolysis during the solvent extractions or under UV exposure leading to a tetrasubstituted furan.

Amino acid derived nitrones were conveniently synthesized in good-to-excellent yields by condensation of alpha-ketoesters with N-benzylhydroxylamine. The cycloaddition reactions of these nitrones with different alkenes were investigated under thermal solvent-free conditions. Considering conversions, yields, and selectivities, alkyl vinyl ethers have proven to be valuable partners to achieve this transformation, which creates a tetrafunctionalized stereogenic quaternary center. From the adducts derived from vinyl ethers, a three-step access to highly functionalized alpha-substituted amino acid derivatives is described.

Cycloaddition reactions occupy a special place in organic synthesis because of the simultaneous creation of several bonds and generation of new stereogenic centers in often highly stereocontrolled ...

N-(β,β-Difluorovinyl)oxazolidin-2-ones were conveniently prepared in good yields in two steps from the parent oxazo-lidin-2-ones. The [3+2]- and [4+2]-cycloaddition-type reactions with electron-deficient partners were investigated as first application of these new enamides. TMSOTf was efficient in promoting these two reactions, and the corresponding heterocyclic difluoro adducts were obtained in high yields.

N-benzyl aspartate nitrones 2, prepared by addition of N-benzylhydroxylamine to dialkyl acetylenedicarboxylates 1, underwent [3 + 2] thermal cycloaddition with a wide range of alkenes to afford isoxazolidines 4 bearing a polyfunctionalized quaternary center. Under these uncatalyzed conditions, the trans stereocontrol observed with vinyl ethers is higher than that obtained with all acyclic activated nitrones reported to date. The first asymmetric access to a type-4 pure adduct was achieved starting from the chiral aspartate nitrone derived from (S)-alpha-methylbenzylhydroxylamine.

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Trimethylsilyl trifluoromethanesulfonate (TMSOTf) was conveniently used to promote the reaction involving N-alkenyloxazolidin-2-ones and activated nitrones, leading to new 4-substituted 5-azaisoxazolidines in good to excellent yields. This TMSOTf-promoted procedure expanded the scope of reaction of N-vinyloxazolidin-2-ones and nitrones in complementary way to the corresponding classical 1,3-dipolar cycloaddition. Some of these adducts could not be obtained under thermal activation.

New isoxazolidines were synthesized in good to excellent yields by 1,3-dipolar cycloaddition of N-vinylamide dipolarophiles and nitrones. Strikingly, solvent-free conditions gave high conversion and yields, shortened reaction time, and minimized degradation products. N-Vinyloxazolidin-2-one and its analogues used in these cycloaddition reactions were conveniently prepared in excellent yields by a modified version of Buchwald's one-step copper-catalyzed vinylation using vinyl bromide. From the adducts, a two-step access to various unsymmetric aspartate derivatives was also described.