Regio- and stereospecific syntheses of syn- and anti-1,2-imidazolylpropylamines from the reaction of 1,1'-carbonyldiimidazole with syn- and anti-1,2-amino alcohols

The regio- and stereospecific conversion of syn- and anti-1,2-amino alcohols to their respective syn- and anti-1,2-imidazolylpropylamines via treatment with 1,1'-carbonyldiimidazole is described. The rationale behind the regio- and stereospecific nature as well as the generality of the reaction is discussed.     

Synthesis of enantiomerically pure anti-1,2-diaryl and syn-1,2-alkylaryl vic-selenoamines

Phenylselenyl benzylcarbanion stabilized by an (S)-2-p-tolylsulfinyl group evolves in a highly stereoselective way in the reactions with (S)-N-(p-tolylsulfinyl)imines at -98 °C affording diastereomerically pure 1,2-selenoamino derivatives in good yields. The syn or anti relationship of the obtained compounds depends on the alkyl or aryl character of the imine. They are easily transformed into enantiomerically pure (1R,2S)-1-aryl[or (1S,2S)-1-alkyl]-2-(phenylseleno)-2-phenylethylamines by reaction with t-BuLi and subsequent methanolysis of the generated sulfinamide derivatives with TFA.     

Highly stereoselective syntheses of syn- and anti-1,2-amino alcohols

The reduction of N-protected amino ketones can be carried stereoselectively to produce either the syn- or anti-amino alcohol diastereomer. Carbamate-protected amino ketones can be reduced predictably and selectively to anti-amino alcohols with LiAlH(O-t-Bu)3 in ethanol at -78 degrees C. N-Trityl-protected amino ketones can be reduced selectively to syn-amino alcohols with LiAlH(O-t-Bu)3 in THF at -5 degrees C.     

Iterative asymmetric allylic substitutions: syn- and anti-1,2-diols through catalyst control

A copper-catalyzed asymmetric allylic boronation (AAB) gives access to syn- and anti-1,2-diols. The method facilitates an iterative strategy for the preparation of polyols, such as the fully differentiated L-ribo-tetrol and protected D-arabino-tetrol. P=protecting group.     

Single route to chiral syn- and anti-2-amino-1,2-diphenylethanols via a new stereodivergent opening of trans-1,2-diphenyloxirane

Oxiranyl ring opening of trans-stilbene oxide gave rise to anti- or syn-2-bromo-1,2-diphenylethanols, using either MgBr(2).Et(2)O or MgBr(2).Et(2)O, NaBr, and KBr with Amberlyst 15, respectively. Starting from optically pure (R,R)-trans-stilbene oxide, (1R,2R)- and (1R,2S)-2-amino-1,2-diphenylethanols were obtained in high yield and ee.     

Facile synthesis of various substituted taurines,especially syn- and anti-1,2-disubstituted taurines,from nitroolefins

Taurine and substituted taurines present a group of important structural elements in many natural products. Various substituted taurines, including 1- and 2-substituted, 1,1-, syn-1,2-, and anti-1,2-disubstituted taurines, were synthesized from the corresponding nitroolefins via Michael addition with thioacetic acid, oxidation with peroxyformic acid, and the catalytic hydrogenation under the catalysis of palladium on carbon or platinum dioxide. It is a general, versatile, and salt-free method for the preparation of substituted taurines, especially for syn- and anti-1,2-disubstituted taurines and some taurines with more bulky substituents. The stereostructures of both syn- and anti-1,2-disubstituted taurines were deduced from the nitroalkyl thioacetates in the Michael addition, which were identified via the Karplus equation analysis and computational analysis, and finally confirmed by the XRD single crystal analysis. The diastereoselectivity in the Michael addition was rationalized with the Cram rule.     

Asymmetric synthesis of syn- and anti-1,3-amino alcohols

The first application of metalloenamines derived from N-sulfinyl imines is reported for the highly diastereoselective addition to aldehydes. Reduction of the beta-hydroxy-N-sulfinyl imine products with catecholborane and LiBHEt3 provides syn- and anti-1,3-amino alcohol derivatives, respectively, with very high diastereomeric ratios.     

Orbital interactions in anti- and syn- tricyclooctadienes and their homoderivatives

Photoelectron spectroscopy and molecular orbital calculations of the Extended Hückel, MINDO/3 and STO-3G Hartree-Fock type have been applied to anti- and syn-tricyclo[4.2.0.0^2,5]octadiene (1 and 2) and their homo and bishomo derivatives. The resulting ordering of the one-electron levels for 1 and 2 are 7a _g ( ₊), [6b _u (), 5b _u (_–)], 4a _u (), 3a _u () and 7a ₁(₊), 5b ₂(), 6b ₂(_–), 3a ₂(), 4b ₁(), respectively. The present results differ substantially from those previously published.     

1,2-Diphospha-3,4-diboretane und 1,3-Diphospha-2,4,5-triborolan: Synthese und Struktur sowie Berechnungen zur Molekülstruktur Über den Einfluß von Substituenten auf die Struktur von 1,2-Diphospha-3,4-diboretan

1,2-Diphospha-3,4-diboretanes and 1,3-Diphospha-2,4,5-triborolane: Synthesis and Structure as well as Calculations on the Molecular Structure On the Effect of Substituents on the Structure of 1,2-Diphospha-3,4-diboretane [2 + 2]-Cyclocondensation reactions led to the synthesis of the 1,2-diphospha-3,4-diboretanes [(t-BuP)₂B₂(NMe₂)₂], 1 a , and [(t-BuP)₂B(NMe₂)B(NiPr₂)], 1 b . Their molecular structures have been determined by X-ray methods, and these are compared with the structure of [(t-Bu)P? BN(iPr₂)]₂, 2 a . Compounds 1 show a folded B₂P₂ four membered ring having tert.-butyl groups in anti-positions. Ab initio calculations on 1,2-diphospha-3,4-diboretanes demonstrate that two conformers with anti-orientation of the substituents at the phosphorus atoms can be expected. These differ by the relative orientation of the almost planar P₂BR groups to the BP₂ plane. The influence of substituents (H and NH₂ at the B atoms, and H and Me at the P atoms) on the ring conformation has been studied. Finally, the first derivative of a 1,3-diphospha-2,4,5-triborolane, 3 a , is reported.