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A combined theoretical and experimental study of a Povarov‐type cycloaddition reaction suggests an asynchronous concerted process that is favored by double Lewis acid activation with BF3·Et2O; endo selectivity was observed in the reactions between N‐(3‐pyridyl)aldimines and styrene, cyclopentadiene, or indene, and substituted tetrahydro‐1,5‐naphthyridine derivatives were obtained in a regio‐ and stereoselective fashion.

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An enantioselective synthesis of tetrasubstituted a-phosphono-a-amino nitriles through asymmetric cyanation of a-ketiminophosphonates catalyzed by Cinchona alkaloids is reported. a-Ket-

Bifunctional Cinchona alkaloid thioureas efficiently catalyze asymmetric nucleophilic addition of nitromethane to ketimines derived from α-aminophosphonic acids to afford tetrasubstituted α-amino-β-nitro-phosphonates. Catalytic hydrogenation of (S)-α-amino-β-nitro-phosphonate 2d gives enantiopure (S)-α,β-diaminophosphonate 3.

The structures of the room-temperature and the lowesttemperature ferroelectric phases of fully deuterated betaine (trimethylammonioacetate) calcium chloride dihydrate have been determined by means of elastic neutron diffraction. In previous structural studies the structural distortions of the incommensurate phase at 130K and the fourfold phase at 90K were analyzed in terms of symmetry modes. The same approach has been applied in the present case and, as a result, a quantitative comparison of the distortions at different temperatures can be performed. This shows that the A 3 (for q ~ 0) and B2u (for q -0) modes, corresponding to the order parameter, are predominant for the three phases. In addition, it has been found that the structure of this primary mode remains essentially unaltered in the three phases. There is only an increase in its global amplitude as the temperature decreases. Accordingly, it can be expected that the structures of the remaining intermediate modulated phases in the transition sequence are similar to that of the first incommensurate phase, except for the change of wavevector values and greater amplitude of the distortion. Crystal data: (CD3)3NCD2COOCaC12.2D20, M r = 279.0, 2 = 0.8308 A, Z = 4, F(000) = 552. At room temperature: Pnma, a--10.95(1), b = 10.15(1), c= 10.82(1)A, V=1203(2)A 3, D x=l.54gcm -3, /z=0.10cm -1, final R = 0.048 for 748 unique observed reflections. At 35K: Pn21a, a = 10.905(9), b = 10.00(1), c =10.80 (1) A, V=1178(2),~ 3, D x=l.57gcm -3, /x--0.11cm -I, final R =0.042 for 1726 unique observed reflections.

2115ization of heterodienes gives pentasubstituted 2,3-dihydropyridines and pyridines in a regioselective fashion.this context, we have been involved in the synthesis of neutral [11] and electron-poor azadienes [9] as well as in the preparation of nitrogen-heterocyclic compounds. [5a,5c,14] As a continuation of our work on the [4ϩ2] cycloaddition chemistry of 2-azadienes, we aim here to explore a new and effective strategy for the preparation of pyridine derivatives through dimerization of electronically neutral 2-azadienes and their reaction with enamines.

The functionalized polyfluorophosphorylated 1-azadienes I have been prepared by a Wittig reaction of ethyl glyoxalate and perfluorophosphorylated conjugated phosphoranes, obtained by reaction of phosphazenes and fluorinated acetylenic phosphonates. Subsequent reduction of both carbon-carbon and carbon-nitrogen double bonds of these 1-azadienes I affords the fluorine-containing β-aminophosphonates II, with the syn β-aminophosphonate being obtained as the major diastereoisomer. Base-mediated cyclocondensation of a diastereomeric mixture of aminophosphonates II leads exclusively to a new type of functionalized trans-γ-lactams III in a diastereoselective way. A computational study has also been used to explain the observed diastereoselectivity of these reactions.