Dedicated to Professor Carmen Nµjera on the occasion of her 60th birthday b-Nitro nitriles are potentially useful intermediates for the synthesis of a variety of bifunctional compounds, including b-amino acids. An intuitive retrosynthetic analysis of these compounds suggests a direct conjugate cyanide addition to nitroalkenes 1 as a straightforward route for such structures. In spite of its apparent simplicity, however, the development of this reaction is restricted by the high tendency of nitroalkenes to polymerize under basic conditions. Consequently, there is only one recent report for use of acetone cyanohydrin as the cyanide source for the conjugate addition to nitroalkenes in its racemic form [1] and a second one for the asymmetric addition, which afforded moderate enantioselectivities and appears to be restricted to (less prone to polymerization) b,b-disubstituted compounds. [2] Taking into account the relative stability of silyl nitronates, we decided to focus on the use of trialkylsilyl cyanides as reagents to obtain b-cyano silyl nitronates 2 as the primary products of the reaction, thereby avoiding the abovementioned polymerization. Moreover, the rich chemistry of silyl nitronates [3] could be eventually exploited beyond the trivial hydrolysis to b-nitronitriles 3. Surprisingly, a survey of the literature reveals that this relatively simple reaction remains hitherto unexplored, and that b-cyano silyl nitronates have never been synthesized. We now wish to report on the development of a practical approach for the asymmetric cyanosilylation of nitroalkenes (Scheme 1).The reaction of (E)-3-methyl-1-nitrobut-1-ene (1 a) with TMSCN (trimethylsilyl cyanide) was chosen as a model case of study. Several types of catalysts were considered as potential candidates for the activation of the reagent and/or the nitroalkene. Initially, cinchona alkaloids were used for the nucleophilic activation of TMSCN.[4] Unfortunately, the reaction proceeded with low conversions after prolonged reaction times, and partial polymerization of the nitroalkene could not be avoided. Moreover, the selectivity was low in all cases, reaching a maximum of 67:33 enantiomeric ratio (e.r.) for a reaction performed with 5 mol % of quinine in nBu 2 O (see Supporting Information).We next explored the behavior of bifunctional thiourea/ tertiary amine catalysts for the simultaneous activation of the nitroalkene (by the thiourea as an hydrogen-bond donor moiety) and the reagent (by the amino nitrogen) [5] (Scheme 2). A higher catalytic activity and a better stereochemical control were expected from these catalysts provided by more ordered catalyst-substrate-reagent complexes I. Catalysts 4 and 5 were totally inactive, suggesting that a more nucleophilic amine is required. On the other hand, bifunctional catalysts 6 and 7 developed by the groups of Soos [6] and Hiemstra, [7] respectively, afforded he expected product 3 a with higher enantiomeric ratios (75:25 and 79:21 e.r., respectively), but the catalytic activity remained very low (conversions < 2...

An efficient and versatile synthesis of novel exo-imidazolidin-2-one dienes is described. This involves the base-assisted condensation/cyclization cascade reaction of the monoimino derivatives of diacetyl with a series of isocyanates. This methodology enables preparation of symmetrical dienes, as long as the substrates have the same N substituent. Moreover, use of different N-substituted starting materials leads to formation of nonsymmetrical dienes. The reactivity of these dienes was evaluated in Diels-Alder reactions, showing a high reactivity.

The synthetic application of 4,5-bis-alkylidene-1,3-oxazolidin-2-ones led to the efficient and regioselective synthesis of 2-(3H)-benzoxazolones and diarylamines with a short methodology. They were also valuable synthons in a total synthesis of naturally occurring carbazoles. New enantiopure 4-oxazoline-2-one and 4-methylene-2-oxazolidinone were prepared via a one-pot microwave (MW)-promoted condensation of α-ketols and an enantiopure isocyanate. These enamides were efficient nucleophiles when added to Michael acceptors to give a series of compounds with quaternary stereocenters in fairly good stereoisomeric ratios. The novel approach for the synthesis of benzofurans and indoles by intramolecular cyclization of enaminones has been applied in the preparation of furobenzofurans starting from benzo-bis-enaminones.

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A new total synthesis of the natural carbazole murrayanine (1) was developed by using the 4,5-dimethyleneoxazolidin-2-one 12 as starting material. The latter underwent a highly regioselective DielsAlder cycloaddition with acrylaldehyde (¼ prop-2-enal; 13) to give adduct 14 (Scheme 3). Conversion of this adduct into diarylamine derivative 9 was carried out via hydrolysis and methylation (Scheme 4). Differing from our previous synthesis, in which such a diarylamine derivative was transformed into 1 by a Pd II -stoichiometric cyclization, this new approach comprised an improved cyclization through a more efficient Pd 0 -catalyzed intramolecular diaryl coupling which was applied to 9, thus obtaining the natural carbazole 1 in a higher overall yield.