MeOH Addition Research Articles

Complexation to FeII, NiII, and ZnII of Multidentate Ligands Resulting from Condensation of 2-Pyridinecarboxaldehyde with α,ω-Triamines: Selective Imidazolidine/Hexahydropyrimidine Ring Opening Revisited

The condensation reaction between 2-pyridinecarboxaldehyde and diethylenetriamine, 3-[(2-aminoethyl)amino]propylamine, and 3,3'-iminobis(propylamine) in a 2:1 molar ratio yields ligands that may be isolated exclusively in the dissymmetric (cyclic) isomeric forms L(A), L(B)/L(B*), and L(C). The template effect of a metal center (Fe(II), Ni(II), and Zn(II)) results in the ring opening of L(C) including one hexahydropyrimidine ring and one (long) propylene bridge. The resulting symmetric bis-Schiff base isomeric form L(C') is stabilized through pentacoordination, yielding [Fe(II)L(C')(NCS)](NCS) (3), [Ni(II)L(C')(NCS)](NCS) (6), and [Zn(II)L(C')(NCS)](NCS) (9). The same metal centers are too bulky to exert a template effect on L(A) including one imidazolidine ring and one (short) ethylene bridge. L(A) acts as a tetradentate ligand yielding [Fe(II)L(A)(NCS)2] (1), [Ni(II)L(A)(NCS)2] (4), and [Zn(II)L(A)(NCS)2] (7). The template effect of the metal center is selective toward the ligand L(B)/L(B*) including a hexahydropyrimidine (imidazolidine) ring and the shorter ethylene (longer propylene) bridge. The Fe(II) cation is small enough to exert a template effect, resulting in the ring opening of L(B)/L(B*). The resulting bis-Schiff base L(B') is stabilized through pentacoordination, yielding [Fe(II)L(B')(NCS)](NCS) (2). Ni(II) is too bulky to promote the ring opening of L(B)/L(B*): L(B) acts as a tetradentate ligand, yielding [Ni(II)L(B)(NCS)2] (5) (the L(B*) isomer is totally converted to L(B)). The coordinative requirements and stereochemical preference of the bulkier Zn(II) cation allow neither the ring opening of L(B)/L(B*) nor the tetracoordination of L(B) or L(B*) but stabilize the novel tetradentate dissymmetric form L(B degrees) in [Zn(II)L(B degrees)(NCS)2].H2O (8) (L(B degrees) results from MeOH addition across the imine bond of L(B)). Density functional theory calculations performed for Ni(II) and Zn(II) complexes of the L(B)/L(B*)/L(B degrees) set of ligands allowed one to compare the relative stabilities of all possible isomers, showing that the most stable ones correspond to those experimentally obtained: isomerization, or methanol addition across the imine bond, of the tetradentate ligand depends on the relative stabilities of all possible isomeric complexes.

Transition structures for MeOH addition to pentadienyl cations and stereochemistry of intramolecular ether cyclization

Three transition structures for MeOH addition to pentadienyl cations were obtained by ab initio quantum mechanical calculations. By applying a force field model of the transition structures with fixed core treatment, we could reproduce the observed stereoselectivity of an intramolecular ether cyclization.

Diethylborylierung und Sulfidierung von ω‐Lactamen

Diethylborylation and Sulfidation of ω‐LactamsSeveral reaction modes of ω‐lactams [A (n = 3), B (4), C (5), D (6), E (7), F (11)] with Et3B are observed between 20 and 110°C. The Et2B lactims (1) having various degrees of association [(1a)x; 1b; (1d)2 (X‐ray structure); 1e; (1f)4] are formed by elimination of 1 mol of ethane. The condensation products [2b; 2c (X‐ray structure)] result by elimination of 1.33 mol of ethane together with the lactim derivatives (3b; 3c). Thermolysis (≥ 125°C) of (1d)2, 1e, and (1f)4 leads to mixtures, in which the compounds 2d, e, f and 3d, e, f, resp., have been identified (NMR, MS). Differences of the thermal behaviour of 1a–f (s‐cis/trans conformers, cis/trans lactims, association degree) are discussed. – From 2b, c and Hacac the N‐acylamidines (4b, c) are obtained, which react with (9‐BBN)2S to yield the monomeric 9‐BBN‐ω‐thiolactims [5b; 5c (X‐ray structure)]. The latter react with MeOH to give the ω‐thiolactams (6b, c) and 9‐MeO‐9‐BBN, from which the 2:2 MeOH addition compound (7)2 (X‐ray structure) is obtained.

Fredericone, neue hochfunktionalisierte Abietanoide aus Blattdrüsen von Coleus fredericii G. TAYL

Fredericon A, B, C, and D, Novel and Highly Functionalized Abietanoids from Leaf‐Glands of Coleus fredericiiFrom the leaf‐glands of the title plant (fam. Labiatae) two novel, genuie spirocycloopropyl‐coleons have been isolated and structurally characterized. Fredericon A (1) bears the unusal 1,1,2‐tricarbonylcyclopropane substructure that renders the molecule very suseptible to nucleophile‐promoted rearrangements. Biogenetically intriguing is the presence of a 3‐acetoxypropyl side‐chain in fredericon B (3). Its formation from the well known isopropyl group is explained by transformation of the latter into a spirocyclopropane, followed by a reductive opening of the cyclopropane and reducation of the aldehyde, MeOH addition to 1, yields fredericon C (5), a derivative of 1H‐phenanthro[3,2‐b]pyran‐7,12(2H,8H)‐dione by two consecutive introlecular nucleophilic openings of the cyclopropane ring and the derived methoxy‐oxirane. Similar methanolysis of a crude fraction of 1, produced, in addition to 5, the fredericon D, a novel derivative of 3H‐phenanthro[3,2‐b]pyran‐2‐(4H)‐one(6).