Zur Theorie der Doppelbindung

Ohne Zusammenfassung     

Additionsreaktionen an der alicyclischen Doppelbindung von Eburnamenin und Apovincamin

Addition reactions on the alicyclic double bond of eburnamenine and apovincamine The addition of alcohols, amines or thiols on the 14, 15-double bond of (?)-eburnamenine ( 3a ) or (+)-apovincamine ( 9a ) yielded the corresponding analogues of vincanol ( 5b-h ), epivincanol ( 7b-d ), vincamine ( 10b-e ) and epivincamine ( 11b-g ) with varying stereoselctivity. The reaction was achieved by addition of hydrogenbromide at ?78° followed by nucleophilic attack, or in the (?)-eburnamenine series also by direct addition of alcohols and thiols under acidic conditions. Without exception the analogues of epivincamine ( 11a-g ) exhibited two carbonyl absorption bands in thier IR. spectra. (?)-Eburnamenine ( 3a ) was obtained from (+)-apovincamine ( 9a ) in a simple one pot reaction.     

Stereoselektive Alkylierung an C(α) von Serin,Glycerinsäure,Threonin und Weinsäure über heterocyclische Enolate mit exocyclischer Doppelbindung

Steroselective Alkylation at C(α) of Serine, Clyceric Acid, Threonine, and Tartaric Acid Involving Heterocyclic Enolates with Evocyelic Double Bonds The chiral, non-racemic title acids are converted to methyl dioxolane-(cf. 13 ), oxazoline-( 4 ) and oxazolidinecarboxylates (cf. 9 ). Deprotonation by Li(i-Pr) ₂N at dry-ice temperature gives solutions of the lithium enolates A–D With exocyclic enolate double bonds. These are stable crough with respect to β-elimination (Scheme 1) to be alkylated with or without cosolvents such as HMPA or DMPU The products are formed in good to excellent yields and, with the exception of the tartrate-derived acetonlde (see Scheme 2), with diastereoselectivities above 90%. While the tartrate-and threonine-derived enolates ( A and B , resp.) are chiral due to the second stereogenic center of the precursors, the serine- and glyceric-acid-derived enolates ( A and B , resp.) are chiral due to the second sterogenic center of the precursors, the serine-nd glyceric-acid-derived enolates are non-racemic due to a tert butyl-substituted (pivalaldehyde-derived) acetal center ( C and D , resp.). The products of alkylation can be hydrolyzed to give α-branched tartaric acid (Scheme 2), allothreonine (Scheme 3), serine (Scheme 4), and glyceric-acid derivatives (Scheme 5) with quaternary stereogenic centers. The configurations of the products are determined by NOE-NMR measurements and by chemical correlation. These show that the dioxolane-derived enolates A and D are alkylated preferentially from that face of the ring which is already substituted (‘syn’-attack), while the dihydrooxazol-and oxazolidine-derived enolates B and C are alkylated from the opposite face (‘anti’-attack). The ‘syn’-attack is postulated to arise from strong folding of the heterocyclic ring due to electronic repulsion between the enolate π-system and non-bonding electron pairs on the heteroatoms (see Scheme 6).     

rac‐5‐Diphenylacetyl‐2,2,4‐trimethyl‐2,3,4,5‐tetrahydro‐1,5‐benzothiazepine and rac‐5‐formyl‐2,2,4‐trimethyl‐2,3,4,5‐tetrahydro‐1,5‐benzothiazepine

rac‐5‐Diphenylacetyl‐2,2,4‐trimethyl‐2,3,4,5‐tetrahydro‐1,5‐benzothiazepine, C₂₆H₂₇NOS, (I), and rac‐5‐formyl‐2,2,4‐trimethyl‐2,3,4,5‐tetrahydro‐1,5‐benzothiazepine, C₁₃H₁₇NOS, (II), are both characterized by a planar configuration around the heterocyclic N atom. In contrast with the chair conformation of the parent benzothiazepine, which has no substituents at the heterocyclic N atom, the seven‐membered ring adopts a boat conformation in (I) and a conformation intermediate between boat and twist‐boat in (II). The molecules lack a symmetry plane, indicating distortions from the perfect boat or twist‐boat conformations. The supramolecular architectures are significantly different, depending in (I) on C—H...O interactions and intermolecular S...S contacts, and in (II) on a single aromatic π–π stacking interaction.     

O‐Benzyl‐N‐tert‐butoxy­carbonyl‐N‐methyl‐l‐tyrosine

The crystal structure of the title compound, alternatively called 3‐[4‐(benzyl­oxy)­phenyl]‐2‐(N‐tert‐butoxy­car­bonyl‐N‐methyl­amino)­propi­onic acid, C₂₂H₂₇NO₅, has been studied in order to ex­amine the role of N‐methyl­ation as a determinant of peptide conformation. The conformation of the tert‐butoxy­carbonyl group is trans–trans. The side chain has a folded conformation and the two phenyl rings are effectively perpendicular to one another. The carboxyl­ate hydroxyl group and the urethane carbonyl group form a strong intermolecular O—H?O hydrogen bond.     

Neue molekulare Indium‐Zinn‐Sauerstoff‐ und Indium‐Zinn‐Natrium‐Sauerstoff‐Chlor‐Cluster

Abstract. The five‐membered heteroelement cluster THF · Cl₂In(O^tBu)₃Sn reacts with the sodium stannate [Na(O^tBu)₃Sn]₂ to produce either the new oxo‐centered alkoxo cluster ClInO[Sn(O^tBu)₂]₃ ( 1 ) (in low yield) or the heteroleptic alkoxo cluster Sn(O^tBu)₃InCl₃Na[Sn(O^tBu)₂]₂ ( 2 ). X‐ray diffraction analyses reveal that in compound 1 the polycyclic entity is made of three tin atoms which together with a central oxygen atom form a trigonal, almost planar triangle, perpendicular to which a further indium atom is connected through the oxygen atom. The metal atoms thus are arranged in a Sn₃In pyramid, the edges of which are all saturated by bridging tert‐butoxy groups. The indium atom has a further chloride ligand. Compound 2 has two trigonal bipyramids as building blocks which are fused together at a six coordinate indium atom. One of the bipyramids is of the type SnO₃In with tert‐butyl groups on the oxygen atoms, while the other has the composition InCl₃Na with chlorine atoms connecting the two metals. The sodium atom in 2 has further contacts to two plus one alkoxide groups which are part of a[Sn(O^tBu)₂]₂ dimer disposing of a Sn₂O₂ central cycle. The hetero element cluster in 2 thus combines three closed entities and its skeleton SnO₃InCl₃NaO₂Sn₂O₂ consists of three different metallic and two different non‐metallic elements.     

5‐Acetyl‐2‐amino‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile and 2‐amino‐5‐benzoyl‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile acetonitrile solvate

The syntheses, X‐ray structural investigations and calculations of the conformational preferences of the carbonyl substituent with respect to the pyran ring have been carried out for the two title compounds, viz. C₁₅H₁₄N₂O₂, (II), and C₂₀H₁₆N₂O₂·C₂H₃N, (III), respectively. In both mol­ecules, the heterocyclic ring adopts a flattened boat conformation. In (II), the carbonyl group and a double bond of the heterocyclic ring are syn, but in (III) they are anti. The carbonyl group forms a short contact with a methyl group H atom in (II). The dihedral angles between the pseudo‐axial phenyl substituent and the flat part of the pyran ring are 92.7 (1) and 93.2 (1)° in (II) and (III), respectively. In the crystal structure of (II), inter­molecular N—H⋯N and N—H⋯O hydrogen bonds link the mol­ecules into a sheet along the (103) plane, while in (III), they link the mol­ecules into ribbons along the a axis.     

4‐Ethynyl‐4‐hydroxycyclohexan‐1‐one and 4‐ethynyl‐4‐hydroxy‐2,3,5,6‐tetramethylcyclohexa‐2,5‐dien‐1‐one

The title compounds, C₈H₁₀O₂, (I), and C₁₂H₁₄O₂, (II), occurred as by‐products in the controlled synthesis of a series of bis­(gem‐alkynols), prepared as part of an extensive study of synthon formation in simple gem‐alkynol derivatives. The two 4‐(gem‐alkynol)‐1‐ones crystallize in space group P2₁/c, (I) with Z′ = 1 and (II) with Z′ = 2. Both structures are dominated by O—H?O=C hydrogen bonds, which form simple chains in the cyclo­hexane derivative, (I), and centrosymmetric dimers, of both symmetry‐independent mol­ecules, in the cyclo­hexa‐2,5‐diene, (II). These strong synthons are further stabilized by C[triple‐bond]C—H?O=C, C_methylene—H?O(H) and C_methyl—H?O(H) interactions. The direct intermolecular interactions between donors and acceptors in the gem‐alkynol group, which characterize the bis­(gem‐alkynol) analogues of (I) and (II), are not present in the ketone derivatives studied here.     

4‐Acetyl‐5‐methyl‐2‐phenyl‐1,2‐di­hydro‐3H‐pyrazol‐3‐one hydrate

The title compound, C₁₂H₁₂O₂N₂·H₂O, is described. Although the keto–enol form of the ligand in solution is known, the compound crystallized in the orthorhombic space group P2₁2₁2₁ with only the monohydrated 1,3‐diketo form. The intermolecular hydrogen bond between the imino N—H group of the ligand and O atom of the water mol­ecule recorded an H?O distance of 1.73 (3) Å.