Synthese von triafulvalen-vorstufen durch ‘carben-dimerisierung’ von 1-halogeno-1-lithiocyclopropanen

Synthesis of Triafulvalene Precursors by ‘Carbene-Dimerization’ of 1-Halogeno-1-lithiocyclopropanes Bi(cyclopropylidenes) 7a , 7c , and 7e are available in a simple one-pot reaction by treating 1,1-dibromocyclo-propanes 5 at ?95° with BuLi and CuCl₂. Attempts towards triafulvalene precursors with good leaving groups are reported. The most promising attempt makes use of 2,2′-bis(phenylthio)-3,3′-bis(trimethylsilyl)-1,1′-bi(cyclopropylidene) (7c) which has been oxidized to give the bis(phenylsulfonyl) derivative 7g. So far, F^?-induced elimination experiments with 7g failed.     

Die Reaktion von 1-Halogeno-1-Lithiocyclopropanen mit CuCl2: Konkurrenz zwischen ‘Carben-Dimerisierung’ und oxidativer Kupplung

The Reaction of 1-Halogeno-1-lithiocyclopropanes with CuCl₂: Competition between ‘Carbene Dimerization’ and Oxidative Coupling The 1-chloro-1-lithiocyclopropanes 2a – d react at low temperature with CuCl₂ to give diastereoisomeric mixtures of oxidative-coupling products 5a – d and of ‘carbene dimers’ 6a–d . The relative amount of 5a – d increases with CuCl₂ concentration and reaction time. Diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoisomers are difficult. The conformational behavior of 1,1′-dichloro-1,1′-bi(cyclopropyls) 5c and 5d is discussed. Contrary to 2a – d , 1-bromo-1-lithiocyclopropanes normally react with CuCl₂ to give ‘carbene dimers’ 6 and no coupling products 5 . So far the only exception is 1-bromo-1-lithio-2-phenylcyclopropane 2e which in the presence of CuCl₂ gives some percents of coupling products 5e besides carbene dimers 6b as main products. An X-ray structure analysis of the predominant diastereoisomer 5e was performed.     

Kupfer(II)-chlorid-katalysierte ‘Carben-Dimerisierung’ von 1-Halogeno-1-Lithiocyclopropanen: Ein einfacher Zugang zu Bi(cyclopropylidenen)

Copper(II)-Chloride Catalyzed ‘Carbene Dimerization’ of 1-Halogeno-1-lithiocyclopropanes: A Simple Access to Bi(cyclopropylidenes) A series of 13 bi(cyclopropylidenes) 11 are prepared in a simple one-pot reaction by halogeno-lithio exchange between 1,1-dibromocyclopropanes 1a – n and BuLi, in most cases at ?95°, to give 1-bromo-1-lithiocyclopropanes 2a – n , followed by treatment with CuCl₂ at low temperature and a simple workup at room temperature (Scheme 3c and Table 1). The yields of bi(cyclopropylidenes) 11 strongly depend on reaction parameters, as explicitly shown for the conversion 1f →→ 11f (Tables 2–8). Mixed couplings between two different carbenoids are possible (Scheme 4), while diastereoselectivity of the active transition-metal complex seems to be low. The structures of bi(cyclopropylidenes) 11 are confirmed by spectroscopic data as well as by X-ray analysis of an isolated crystalline diastereoisomer of 11k (Fig. 1).     

Synthese von ‘D-Isothreonin’ und ‘L-Alloisothreonin’ aus L-Alanin

Synthesis of ‘D -Isothreonine’ and ‘L -Alloisothreonine’ Starting from L -Alanine Starting from L -alanine, ‘D -isothreonine’ ( = (2R, 3S)-3-amino-2-hydroxybutanoic acid) and ‘L -alloisothreonine’ ( = (2S, 3S)-3-amino-2-hydroxybutanoic acid) were synthesized.     

Stereoselektive c-glycosidsynthese durch titan-(iv)-katalysierte addition von silylenolethern an 2-acyloxy-3-keto-glycale

C-Glycosides are stereoselectively formed by the titan-(IV)-catalysed addition of silyl enolethers $\text{2}$ to 2,4,6-tri-O-acyl-1-deoxy-D-erythro-hex-1-enopyran-3-uloses $\text{1}$ followed by elimination of the 4-acyloxy substituent. Cyclohexenyl silylether $\text{2a}$ reacts with 2-acetoxy-3-keto-glycal derivative $\text{la}$ forming only one product $\text{3a}$. Thus, the reaction seems to be diastereospecific with respect to both new chiral centers of the product.     

Synthese von ‘Push-Pull’-Diacetylenen

Synthesis of ‘Push-Pull’ Diacetylenes The first synthesis of push-pull diacetylenes of type 1 is described. Reaction of perchlorobutenyne ( 8 ) with two equivalents of dialkylamine, followed by dechlorination using two equivalents of butyllithium gives lithio-dialkylamino-diynes 7 . Final acylation of these intermediates leads to push-pull diacetylenes 1b–1e in good yields. The method allows the introduction of both push and pull substituents in a simple one-pot-procedure. In addition, 1a is prepared by hydroxymethylation of lithio-morpholino-diyne 7c , followed by oxidation with manganese dioxide in acetone.     

Synthese von ‘Push-Pull’-Oligoacetylenen

Synthesis of ‘Push-Pull’-OligoAcetylenes ‘Push-pull’ triacetylenes 11a , b , c , as well as ‘push-pull’ tetraacetylene 13b have been prepared by reaction of the corresponding trichloroene(oligoinyl)amines 9 and 10 with 2 mol-equiv. of BuLi followed by acylation. The sequences (Schemes 3 and 4) are very simple and straightforward, they could in principle be applied to the synthesis of ‘push-pull’ pentaAcetylenes 15 and hexaacetylenes 17 (Scheme 5). Main limitations are the moderate yields as well as the low thermal stability of push-pull oligoacetylenes.     

Herstellung von ‘Semialdehyd’-Derivaten von Asparaginsäure- und Glutaminsäure durch Rosenmund-Reduktion

Preparation of ‘Semialdehyde’ Derivatives of Aspartic and Glutamic Acid via the Rosenmund Reduction Suitably protected aspartic-acid ‘β-semialdehyde’ and glutamic-acid ‘γ-aldehyde’ derivatives can be obtained, in good yield by Rosenmund reduction of the corresponding acid chlorides. Benzyloxycarbonyl (Z) and (tert-butoxy)carbonyl (Boc) protecting groups are not affected under these reaction conditions. The sensitive aldehydes, which are obtained in higher purity than by hydride reductions, can directly be used for further transformations like aldol-type reactions.     

Der ‘Push-Pull’-Effekt von ‘Push-Pull’-Oligoacetylenen. Eine 13C-NMR-Untersuchung

The ‘Push-Poll’ Effect of ‘Push-Pull’ Oligoacetylenes. A ¹³C-NMR Investigation According to ¹³C-chemicaI shifts of ‘push-pull’ oligoacetylenes 1 – 4 , the ‘push-pull’ effect (i.e. π delocalization induced by ‘push-pull’ substituents) rapidly decays in this series. To correct for other than π -charge-density effects, Δδ values of symmetrically placed C-atoms of the oligoacetylene chain are discussed. Stereoelectronic resteffects (SER) of the substituents on terminal C-atoms of PP-ketones 1a – 3a and PP -esters 1b – 4b are estimated from the residual Δδ of the asymptotes of Fig. 3. Fig. 4 convincingly shows that Δδ values are dramatically decreasing with increasing number n of acetylene units between the push and pull substituents. Assignment problems of ‘push-pull’ triacetylenes 3 have been solved by ¹³C labelling of the CO group of 3a .     

Synthese von ‘Push-Pull’- Eninen

Synthesis of ‘Push-Pull’ Enynes ‘Push-pull’ enynes 1a–1f are easily available by Pd catalyzed coupling of stannyl-ynamines 15 and silylynamines 16 with β-iodo-enones 8 (Schemes 7 and 8).     

Versuche zur Synthese von ‘Push-Pull’-Diacetylenen

Attempted Synthesis of Push-Pull Diacetylenes Two alternative synthesis of push-pull diacetylenes of type 1 (5-amino-2,4-alkadiynals) are investigated. A bromination-dehydrobromination sequence starting with 5-dimethylamino-2,4-pentadienal ( 2 ) as well as the application of the well-known Cadiot-Chodkiewicz coupling reaction give new intermediates 3–5 , and 7 and 8 , respectively, but fail to give the target molecules 1 .     

Rh(I)-katalysierte Umlagerungen von 3,4-Diacycloxy-1,5-hexadiinen; synthese von (E)-4-acyloxymethyliden-2-cyclopenten-1-onen

Rh(I)-Catalysed Rearrangements of 3,4-Diacyloxy-1,5-hexadiynes; Synthesis of (E)-4-Acyloxymethyliden-2-cyclopenten-1-ones The 3,4-diacyloxy-1,5-hexadiynes 3, 6 and 8 which were synthesized according to a known, slightly modified procedure react with [Rh(CO)₂Cl]₂ at 100° in chloroform with formation of the (E)-4-acyloxymethyliden-2-cyclopenten-1-ones 4, 7 and 9 (Schemes 2, 3 and 4), respectively. DL - and meso- 3 as well as trans- and cis- 8 , give the same (E)-isomers 4 and 9 , respectively. 3,4-Diacetoxy-3, 4-dimethyl-1, 6-diphenyl-1,5-hexadiyne ( 10 ) produces with the same catalyst 2,6-diacetoxy-3, 4-dimethyl-1,6-diphenylfulvene ( 11 ) (Scheme 5). A mechanism for the formation of the cyclopentenones is proposed in Scheme 6.     

Synthese neuer Heptafulvene,Röntgenstrukturanalyse von ‘8,8-(1′,4′-Dioxotetramethylen)heptafulven’(2-(Cyclohepta-2,4,6-trien-1-yliden)cyclopentan-1,3-dion)

Synthesis of New Heptafulvenes; X-Ray Analysis of ‘8,8-(1′,4′-Dioxotetramethylene)heptafulvene’ (2-(Cyclohepta-2,4,6-trien-1-ylidene)cyclopentane-1,3-dione) Experimental procedures for the synthesis of heptafulvene ( 3a ), 8,8-tetramethylene heptafulvene ( 3c ) and ‘8,8-(1′,4′-dioxotetramethylene) heptafulvene’ (2-(cyclohepta-2,4,6-trien-1-ylidene)-cyclopentane-1,3-dion; 3d ) are described. The most important sequences include a low-temperature reaction of tropylium salts with lithium or Grignard carbenoids (Scheme 1) to give 3a and 3b as well as hydride abstraction from substituted cycloheptatrienes followed by deprotonation to give 3c and 3d . Limitations of these sequences are discussed. Two other heptafulvenes 3h and 3i are available by silylation of heptafulvenolates according to well-known procedures. NMR-Spectroscopic evidence as well as an X-ray analysis of 3d are presented. Compound 3d is a relatively polar heptafulvene with a planarised seven-membered ring as well as a partly delocalized π system.     

Einelektronen-Redoxreaktionen von 4-(1-Pyridinio)phenolat-Betain: ESR/ENDOR-Charakterisierung seiner Radikalionen und ‘Batterie-Effekt’

One-Electron Redox Reactions of 4-(1-Pyridinio)phenolate Betaine: ESR/ENDOR Characterization of its Radical Ions and ‘Battery Effect’ Blue zwitterionic 2,6-Di(tert-butyl)-4-(2,4,6-triphenyl-1-pyridinio)phenolate 1a can be reduced to its blue-green radical anion ${\bf 1}^{- \atop \dot{}}$ using alkaline metals, and oxidized to its colorless radical cation 1 by Ag(OOCCF₃) or electrochemically. ESR/ENDOR spectra of their aprotic THF solutions indicate predominant spin population either in the pyridinium (${\bf 1a}^{- \atop \dot{}}$) or in the phenolate ring (${\bf 1a}^{+ \atop \dot{}}$). Reduction with other alkaline metals Li, Na, or Cs yields no changes in the ESR/ENDOR signal patterns, i.e. provides no indication of radical ion pair formation. The cyclovoltammetrically determined first reduction and oxidation potentials at ?1.11 V and +0.26 V, respectively, are both reversible and, in principle, allow to construct a molecular battery.     

Rhodium(I)-Catalyzed ‘Metallo-Ene’ Cyclizations/β-Eliminations

Octadienyl carbonates 5 provide cyclic 1,4-dienes 6 when treated with Rh¹ complexes (1–10 mol-%) at 80°. Similar cyclization of cyclohexenyl acetate 8 affords cis- fused hexahydroindene 9 . Analogous ring closures of nonadienyl carbonate 10 yield preferably the cis-divinypyrrolidine 11 with Rh¹ catalysis but the trans-isomer 12 when catalyzed by Pd⁰. Azaoctadienyl carbonate 5a undergoes elimination with [RhH(PPh₃)₄] (5 mol-%, 80°) in MeCN giving acyclic triene. 7 .