Jew data are reported concerning the luminescence of PbI, single crystals submitted to thermal treatments. Both the analysis of this luminescence by time-resolved spectroscopy and its dependence on the thermal treatment and the perfection of the lattice indicate the existence of complex luminescent centres. By extending the photoconduction and absorption studies into the near IR, supplementary dat,a are obtained concerning the levels induced in the energy band gap due to the centres creat,ed by t'hermal treatment and irradiation.On prksente des donnees nouvelles concernant la luminescence des monocristaux de PbI, soumis aux traitements thermiques. L'analyse de cette luminescence par spectroscopie A resolution temporelle e t sa dbpendence de la temperature de traitement thermique e t de la perfection du rBseau cristallin indiquent l'existence des centres complexes de luminescence. On prksente aiissi les r6sultat.s des Btudes de photocondwtion e t d'absorption dans le prouhe IR concernant les nouveaiix niveaux d'hnergie dans la bande interdite dtis aux centres crbbs par le traitement thermique et, l'irradiation.

Rhodium(II)-acetate-catalyzed decomposition of either 1,3-cyclohexanedione phenyliodonium ylide or 5,5-dimethyl-1,3-cyclohexanedione phenyliodonium ylide in the presence of alkyl halides yields the corresponding 3-alkoxy-2-halocyclohex-2-enones via a 1,4 alkyl group migration shown to be concerted and intramolecular. In the case of (S)-alpha-phenethyl chloride, the rearrangement proceeds with essentially 88.6% retention of configuration. Theoretical calculations at the B3LYP/6-31G level reveal an activation energy of 5.4 kcal/mol for the process. A Claisen-like rearrangement occurs in the case where allylic halides, such as dimethylallyl or methallyl chorides, are used. The mechanistic pathway proposed for these processes involves addition of the halogen atom of the alkyl or allyl halide to the rhodium carbenoid from the iodonium ylide to yield a halonium intermediate that undergoes halogen to oxygen group migration. Aryl halides, such as chloro-, bromo-, iodo-, and fluorobenzene, behave differently under the same reaction conditions, yielding the product of electrophilic aromatic substitution, namely, the 2-(4-halophenyl) 1,3-cyclohexanedione.

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The regiochemistry of the [3+2] cycloaddition reactions between 4‐R‐phenacylpyridazinium ylides and acrylonitrile has been studied. Theoretical and experimental studies have been performed, both of which show that the reaction is regiospecific. Four new tetrahydropyrrolopyridazine heterocycles have been obtained. The structures of the new compounds were established by elemental (C,H,N) and spectral analyses (IR, 1H and 13C NMR, MS).