Keywords: Lewis bases / Phosphorus / Samarium / Radicals / Cyclization / Lithium Tripyrrolidinophosphoric acid triamide (TPPA) can replace carcinogenic HMPA as a Lewis basic additive in many reactions involving samarium ketyls. In most cases, yields and selectivities of cyclizations of (het)aryl, alkenyl, and alkynyl

In this report we describe the synthesis of differentially functionalized pyridine derivatives 3 and the related 3-bromosubstituted pyridines 11. Dissociation of 6H-1,2-oxazine precursors (1a, 1b, 5, 6, or 12) in situ, mediated by boron trifluoride-diethyl ether, generates the azapyrylium intermediates A, which undergo hetero-Diels-Alder reactions with various mono-and disubstituted alkynes 2. In general, these pyridine syntheses proceeded with high efficiencies and were very flexible with respect to all positions in the pyridine cores. For the 3-phenyl-substituted pyridine derivatives 3a-3j and 11a-11f the best results were obtained by a new microwave-assisted protocol, which is clearly superior to the previously used conventional procedure at low temperature in dichloro-

New conditions for dearomatizing samarium-ketyl (hetero)arene cyclizations are reported. In many examples of these samarium diiodide-mediated reactions, lithium bromide and water can be used as additives instead of the carcinogenic and mutagenic hexamethylphosphoramide (HMPA). The best results were obtained for the cyclizations of N-acylated indole derivatives delivering the expected indolines in good yields and excellent diastereoselectivities. A new type of cyclization delivering indolyl-substituted allene derivatives is also described. The scope and limitations of the lithium bromide/water system are discussed.

SummaryStarting from γ-ketoesters with an o-iodobenzyl group we studied a palladium-catalyzed cyclization process that stereoselectively led to bi- and tricyclic compounds in moderate to excellent yields. Four X-ray crystal structure analyses unequivocally defined the structure of crucial cyclization products. The relative configuration of the precursor compounds is essentially transferred to that of the products and the formed hydroxy group in the newly generated cyclohexane ring is consistently in trans-arrangement with respect to the methoxycarbonyl group. A transition-state model is proposed to explain the observed stereochemical outcome. This palladium-catalyzed Barbier-type reaction requires a reduction of palladium(II) back to palladium(0) which is apparently achieved by the present triethylamine.

In addition to the transformation of the prepared 1,2‐diketones into quinoxalines, their conversion into imidazole, thiophene and 4‐oxoalk‐2‐enoate derivatives is described.