Electron-deficient 1- and 2-azabuta-1,3-dienes are reagents intrinsically able to provide a wide range of cyclic and acyclic N-containing building blocks. Depending on their substitution, they behave as dienes for Diels-Alder reactions, as partners for [4+1], [3+2], [2+2]-cycloadditions, for aziridinations and as electrophiles for 1,2 and 1,4-additions. Nowadays, they are a very versatile family of compounds, despite their usual instability and complex reactivity. Four decades of research in this challenging area are reviewed in this critical review: their synthetic aspects and their reactivity towards a wide range of dienophiles, dipoles and nucleophiles are described as well. The introduction focuses on their electronic properties in order to get a clear picture of their reactivity (190 references).

Trialkyl and silylated dialkyl phosphites were evaluated as phosphorus nucleophiles for the addition to quinolines in a strong acidic medium allowing consecutive 1,4- and 1,2-addition breaking up the aromatic stabilisation, thereby leading to 2,4-diphosphono-1,2,3,4-tetrahydroquinolines in one single reaction step in moderate to good yields (2-84%).

This paper presents the synthesis of epibatidine analogues by a straightforward one-pot method for the synthesis of 7-azabicyclo[2.2.1]heptane-1-carbonitriles, starting from cyclohexanones bearing a leaving group at the 4-position. In situ imine formation, followed by reversible cyanide addition, al-

The 1,4-and 1,2-addition of phosphites to a,b-unsaturated hydrazones was investigated. When silylated phosphites and trialkyl phosphites were compared, trialkyl phosphites gave better conversions and subsequently higher yields. A variety of hydrazones were evaluated as substrate in this reaction, which yield 3-phosphonyl-1-hydrazinoalkyl phosphonates.a-Hydrazinoalkyl phosphonic acids 1 ( Figure 1) and their derivatives have been found to have an interesting protecting effect against the phytotoxic action of chloroacetanilide herbicides. 1 Limited research was performed to establish a general route to this type of compounds. 2 Among the specific methods, the lithium perchlorate/diethyl ether catalyzed multicomponent reaction of an aldehyde, a hydrazine, and silylated phosphite 2e or the binary reagent (MeO) 3 P/Me 3 SiCl 2f seems to be the most straightforward. However, this method is only applicable to aliphatic aldehydes. Figure 1 a-Hydrazinoalkyl phosphonic acidAs a continuation of our studies on the behavior of different phosphorus nucleophiles and the chemistry of azaheterocyclic phosphonates, 3 the addition of silylated phosphites and trialkyl phosphites to a,b-unsaturated hydrazones 2 is presented in this paper (Scheme 1). In this reaction, two phosphonate moieties are introduced in one single reaction to form 3-phosphonyl-1-hydrazinoalkyl phosphonates 3. Our previous research showed that both reagents are able to perform a tandem 1,4-1,2-addition to a,b-unsaturated imines. 4,5 A mechanistic study proved a different reactivity of both phosphorus reagents. Trialkyl phosphites show a higher tendency to perform 1,4-addition than 1,2-addition, where a reverse reactivity is noticed with silylated phosphites. To evaluate the scope of these reactions, hydrazones 2, which were anticipated to be much less reactive compared to imines, have now been evaluated as possible substrates. Scheme 1 Synthesis of 3-phosphonyl-1-hydrazinophosphonates 3To synthesize the substrates 2, an a,b-unsaturated aldehyde was dissolved in methanol in the presence of one equivalent of the hydrazine or hydrazide. After one hour at 0°C, the solvent was evaporated in vacuo and the products were recovered in excellent yields (95-99%).The first part of the research comprised the evaluation of silylated phosphite as a phosphorus nucleophile and was based on the work of Afarinkia and co-workers for the synthesis of a-aminophosphonates. 6 O-Silylation of dialkyl phosphite provided the more nucleophilic s 3 l 3 reagent. 7 In these experiments the hydrazone 2 was dissolved in dry dichloromethane, and 5 equivalents of silylated phosphite were added. This mixture was heated to reflux temperature after which 0.5 equivalents of sulfuric acid were added.Follow-up of the reaction by 31 P NMR (whenever possible, conversions were calculated from integrations in the 31 P NMR) had shown a very slow and incomplete conversion. 8 Imines, on the other hand, showed vigorous reaction upon addition of sulfuric acid (the solvent starts to boil) and the reactions were ...

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