ALBERT

Notes: On treatment with H2SO4/MeOH, epimerization of hexamethyl cis-5,6-dihydroxycobyrinate c,8-lactam (3) takes place quantitatively at C(6), yielding the corresponding trans-diol 4. The corresponding lactone 7, whose structure has been established by X-ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions.

Notes: The titanates derived from α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOLs, prepared from tartrate) act as catalysts for enantioselective additions of dialkylzinc compounds to aldehydes. For the standard reaction chosen for this investigation of the mechanism, the addition of diethylzinc to benzaldehyde, there is very little change of selectivity with different aryl substituents on the TADDOLate ligands (Tables 2-4, examples). With 0.02 to 0.2 equiv. of the chiral titanates, selectivities above 90% are observed only in the presence of excess tetraisopropyl titanate! According to NMR measurements (Fig. 2), the chiral bicyclic titanate and the achiral titanate do not react to give new species under these conditions. From experiments with different stoichiometries of the components, and with different achiral or chiral OR groups on the Ti-atom of the seven-membered ring titanate, it is concluded (i) that a single chiral titanate is involved in the product-forming step, (ii) that the bulky TADDOLate ligand renders the Ti-center catalytically more active than that of (i-PrO)4Ti, due to fast dynamics of ligand exchange on the sterically hindered Ti-center (Table 5, Fig. 3), and (iii) that the role of excess (i-PrO)4Ti is to remove - by ligand exchange - the product alkoxides (R*O) from the catalytically active Ti-center (Scheme 4, Table 6). Three new crystal structures of TADDOL derivatives (two clathrates with secondary amines, and a dimethyl ether) have been determined by X-ray diffraction (Figs. 5-7), and are compared with those previously reported. The distances between the C(aryl)2O oxygen atoms in the C2- and C1-symmetrical structures vary from 2.58 to 2.94 Å, depending upon the conformation of their dioxolane rings and the presence or absence of an intramolecular H-bond (Fig. 8). A single-crystal X-ray structure of a spiro-titanate, with two TADDOLate ligands on the Ti-atom, is described (Fig. 9); it contains six different seven-membered titanate-ring conformations in the asymmetric unit (Fig. 10), which suggests a highly flexible solution structure. The structures of Ti TADDOLate complexes are compared with those of C2-symmetrical Ru, Rh, and Pd disphosphine chelates (Table 7). A common topological model is presented for all nucleophilic additions to aldehydes involving Ti TADDOLates (Si attack with (R,R)-derivatives, relative topicity unlike; Fig. 11). Possible structures of complexes containing bidentate substrates for Ti TADDOLate-mediated ene reactions and cycloadditions are proposed (Fig. 12). A simple six-membered ring chair-type arrangement of the atoms involved can be used to describe the result of TADDOLate-mediated nucleophilic additions to aldehydes and ketones, with Ti, Zr, Mg, or Al bearing the chiral ligand (Scheme 6). A proposal is also made for the geometry of the intermediate responsible for enantioselective hydrogenation of N-(acetylamino)cinnamate catalyzed by Rh complexes containing C2-symmetrical diphosphines (Fig. 13).

Notes: Reactions of 5H,2λ5-Azaphospholes with Arylazocarbonitriles and Dialkyl AcetylenedicarboxylatesAzaphospholes 1a-c react with activated arylazocarbonitriles to 1,5,2λ5-diazaphosphorines 2a-c and 3a-c. The reaction of 1a-c with diethyl or dimethyl acetylenedicarboxyiates yields 7H-1,4λ5-azaphosphepines 4a-c. The structures of 2b, 3a, and 4a are established by an X-ray diffraction analysis.

Notes: Treatment of ten monocyclic dienols 8-11 with an excess of fluorosulfonic acid in 2-nitropropane at -90° afforded diastereoisomeric mixtures of racemic tricyclic ethers 12-14 in 81-91% yield (see tables 1 and 2). These transformations represent further examples of biomimetic acid-mediated cyclisations in which an OH group serves as the internal nucleophilic terminator. A non-synchronous process is postulated, and the examples described strongly re-inforce our working mechanistic hypothesis, whereby the stereochemical course of cyclisation is directed by the orientation of the side chain vicinal to the intermediate cyclohexyl cation (see Schemes 4 and 5). It is also demonstrated that the efficiency of this process is independent of the nature of the OH group, which may be primary, secondary, or tertiary. In addition, the organoleptic properties of 12-14, Me homologs of known odorants such as Ambrox® ((-)-3a) and its diastereoisomer, are briefly discussed.

Notes: The reaction of 2-(1-phenylvinyl)aniline and 4-chloro-2-(1-phenylvinyl)aniline with acetophenone derivatives, 1-(naphthalen-1-yl)ethanone and 1-(furan-2-yl)ethanone in toluene at 110-115° with toluene-4-sulfonic acid as a catalyst leads in good-to-excellent yields to the 2,2-disubstituted 1,2-dihydro-4-phenyl-quinolines 1-18 (Scheme 1, Table). The structure of the new racemic 1,2-dihydroquinolines 1-18 is determined by NMR spectroscopy. A reaction mechanism proceeding via a 6π-electrocyclic rearrangement of 2-(1-phenylvinyl)anils 19 as the key step is proposed for the formation of these compounds (Scheme 1). The scope and limitations of the novel methods are discussed (Scheme 2).

Notes: The readily available 5-nitrospiro[2H-benzimidazole-2,1′-cyclohexane] (1) was converted into the carbonitrile 5 and the 4-phenylthio derivative 4. The NO2 or the PhS substituents in 4 could be replaced regiospecifically by reaction with Me3SiN3 or NaN3, respectively. The 5-azido derivative 8, resulting from NO2-group replacement was made to cyclize photolytically to give the angular spiro[cyclohexane-imidazophenothiazine] 18. The azide 9 obtained from the PhS replacement in 4 cyclized spontaneously to give the angular spiro[cyclohexane-imidazobenzoxadiazole] 10 which, on reductive hydrolysis, furnished benzofurazan-4,5-diamine 14. The diamine 14 was converted by conventional methods into a imidazobenzoxadiazole 15, oxadiazoioquinoxaline 16, and selenadiazoloxadiazole 17. The carbonitrile 5 was converted, in simple steps, into the ‘stretched-out’, angular pteridine and purine analogues, 25 and 28, respectively.

Notes: Synthesis of Pyranol [3,2-b][1]benzopyrans from 1-NitroglycalsA synthesis of pyrano[3,2-b][l]benzopyrans β-addition of salicylic aldehyde to 1-nitroglycals, followed by a Henry reaction, is described. This sequence gave the cis-annelated pyranobenzopyranes 9 and 11 from 5 in 54 and 9% yield, respectively, demonstrating the pronounced diastereoselectivity of the β-addition. Reductive denitration of the crude product mixture yielded 14(75%), 15(15%), and 16(7%), which were oxidized to the aryl ketones 20 and 21, respectively. Reduction of 20 (NaBH4) gave exclusively 15. The ketone 20 was deprotected to 22 and 23.

Notes: A variety of model compounds for the pyrimidinediyl-based rigid-rod polyamide poly[imino-(pyrimidine-2,5-diyl)-imino-tetraphthaloyl] (PPYMT) was prepared, in order to compare their conformations to several model compounds of the related, fully aromatic polymer poly(p-phenyleneterephthalamide) (PPTA). In particular, the structures of N-(2-pyrimidyl)benzamide (PYMB) and its complexed form bis[(N-pyrimidin-2-yl)benzamide]nickel(II) dichloride (NiPYMB) were determined by X-ray diffraction. The molecular packing in these crystals provides us with a model for the possible ‘cross-linking’ of PPYMT fibers. The structures of the trimer model compounds N,N′ -bis(2-pyrimidyl)terephthalamide (PYTA) and N,N′ -bis(benzoyl)-2,5-diaminopyrimidine (BDAP) yield information about the conformation of PPYMT chains and are compared to analogous model compounds of PPTA.

Notes: A New and Simple Method for the Synthesis of Spirocyclic la-QuinolinesThe reaction of anilines with (+)-(R)-pulegone in toluene at temperatures between 125 and 150° with 4-toluenesulfonic acid or I2 as catalysts leads to diastereoisomeric mixtures of spiro[cyclohexane-1,2′(1′H)-quinoline] derivatives (see 1-4, Scheme 1; Table). The diastereoisomers are separated by column chromatography, and the structure of the single isomers is determined by NMR-spectroscopic methods. A reaction mechanism proceeding via several 6π-electrocyclic rearrangements and H-shifts is proposed for the formation of 1H-quinolines 1-4 (Scheme 2). This mechanism is in accordance with the results of the reaction of 2-isopropenylaniline with 3-methylcyclohexanone which leads to a stereoisomeric mixture of 3,4′-dimethylspiro[cyclohexane-1,2′(1H)-quinolines] (Scheme 3).

Notes: The syntheses of thiazole and fused thiazolo derivatives 2-4, 6-8, 10a-11b, 13-16 from heterocylic isothiocyanates 1, 5, 9, and 12 bearing an ortho ester group and bifunctional reagents, such as substituted propargylamines, is described. Different regioselectivity of intramolecular nucleophilic attack of the thiourea S-atom on the C ≡ C bond, resulting in the formation of both thiazolo and thiazino derivatives, as well as NMR structure elucidation are discussed.