NMR-Spectroscopic Investigations of Potentially Planarized Nonafulvenes

¹H- and ¹³C-NMR spectra of nonafulvene 1e and nonafulvenes 2 and 3 have been assigned, high-resolution ¹H-NMR spectra of 2 (600 MHz, Fig. 3) and of 3 (400 MHz, Fig. 2) have been analyzed, and the data are compared with those of other nonafulvenes (Tables 1–6). Generally speaking, according to their spectroscopic behavior, four classes of nonafulvenes (A–D) may be distinguished (Fig. 1). The investigation shows that compounds 1e and 3 belong to class A, being characterized by ¹H-chemical shifts around 6 ppm, strongly alternating ³J(H,H) and ¹³C chemical shifts in the range of 123 to 130 ppm, thus existing in the olefinic form with a non-planar nine-membered ring. On the other hand, 2 is the first nonafulvene of class D, being characterized by ¹H chemical shifts in the aromatic range, large ³J(H,H) values of the same size, and ¹³C chemical shifts around 110 ppm. Since NMR parameters are virtually not influenced by temperature (?50° to 50°) or solvents, it is concluded that 2 exclusively exists in the dipolar structure 2 ^± with a planarized nine-membered ring. According to Fig. 4, these classes (and their spectroscopic data) are linked by 10,10-bis(dimethylamino)nonafulvene ( 1c ; and its temperature-dependent NMR parameters): for 1c , a temperature-dependent equilibrium 1c?1c ^± had earlier been established.     

Substituenteneffekte auf die NMR-Spektren von Pentafulvenen. (13C, 13C)-NMR-Kopplungskonstanten (1J(C,C))

Substituent Effects on NMR Spectra of Pentafulvenes. ¹³C, ¹³C-NMR Coupling Constants (¹J(C, C)) ¹H- and ¹³C-NMR spectra of 6-monosubstituted pentafulvenes 1 – 8 have been analysed, and ¹J(C, C) coupling constants have been determined from ID-inadequate spectra of ¹³C satellites. It turns out that ¹³C,¹³C coupling constants of the ring C-atoms, and especially J(1,2)/J(3,4) and J(2,3), reflect the extent of π delocalisation in the fulvene ring. With increasing electron-donating capacity of the substituent R, J(1,2)/J(3,4) values are decreasing, while J(2,3) (and J(1,5)/J(4,5) as well) are increasing, and linear correlations of Hammett substituent constants σ⁺ and ¹J(C,C) values are obtained.     

Der Mechanismus der Umlagerung substituierter Aminoacrylderivate

Thioacetic acid and dithioacetic acid react with alkynederivatives of the type (CH₃)₂N? C?C? CO? R ( 1 ) in the same way as other carboxylic acids: The addition to dimethylaminopropinal ( 1a ) at low temperatures yields, after rearrangement of the very instable primary adducts, Z-3-acetoxy-N,N-dimethyl-thioacrylamide ( Z-16 ) and Z-3-thioacetoxy-N,N-dimethylthioacrylamide ( Z-17 ) respectively. The structure of the two compounds can be proved by spectroscopic evidence of 16 and 18 , the latter being formed by elimination of thioketene from 17 . According to the distribution of S-atoms in 16 and 17 , two reaction pathways including 4-membered rings can be ruled out. Thus the rearrangement of 3-acyloxy-N,N-dimethyl-acrylamides most probably proceeds by a mechanism including a dipolar six-membered intermediate. This mechanism cannot be valid for the rearrangement of the adducts 2 of hydrohalogen acids, alcohols and amines to the alkyne-derivatives 1 . The acid-catalysed reaction of 3-chloro-3-dimethylamino-propenal ( 2 , X?Cl), labelled at position 1 with ¹³C, yields 3-chloro-N,N-dimethyl-acrylamide ( 3 , X?Cl), containing the label exclusively at position 3 . This result supports a mechanism including an immonium-oxetene 21 (X?Cl) as intermediate. - The experiments are in accord with kinetic investigations.     

Chloracylierung und Bromacylierung von Carbonylverbindungen. IV. Bildungsmechanismus von Carbonsäure-(1-halogenalkyl)estern

Chloroacylation and bromoacylation of carbonyl compounds IV. Investigations of the reaction mechanism The kinetics of the Lewis acid catalyzed reaction between acyl chlorides and carbonyl compounds (especially aldehydes) is investigated by ¹H-NMR.-spectroscopy. With acetyl chloride as starting material a second order reaction is observed; the rate of the reaction increases in polar solvents as well as with increasing electron-donating capacity of the aldehyde. - With benzoyl chloride as starting material the reaction is first order with respect to benzoyl chloride, but zero order with respect to the aldehyde. The reaction rate is strongly influenced by the substituents of the benzoyl chloride. - Two polar reaction mechanisms which are in accord with these results are outlined and discussed.     

Chloracylierung und Bromacylierung von Carbonylverbindungen. II. Analyse der Nebenprodukte

Chloroacylation and bromoacylation of carbonyl compounds II. Structure of the by-products The structures of the by-products formed in the reaction between paraformaldehyde and acetyl chloride as well as between acetaldehyde and acetyl chloride are elucidated. Optimum conditions for a high yield of the (α-chloroalkyl) ester 1 were obtained by variation of structure and reaction parameters. A speculative reaction scheme of the formation of by-products is discussed.     

Neue Wege zu Pentalen-Vorstufen

New Pathways to Precursors of Pentalene Pentalene dimers 2 and 3 are easily available in moderate yields by CuCl₂-induced oxidative coupling of dilithium-pentalenediide ( 5 ) (Scheme 1). On the other hand, NBS bromination of 1,5-dihydropentalene ( 4 ) or of 1,2-dihydropentalene ( 8 ) gives unstable 1-bromo-1,2-dihydropentalene ( 9 ), while subsequent in-situ elimination with Et₃N exclusively gives syn-cis-pentalene dimer 2 in moderate yields (Scheme 3). NMR-Spectroscopic evidence for compounds 2 , 3 , and 9 is presented, and mechanistic alternatives for the formation of pentalene dimers 2 and 3 are discussed.     

Neue Bi(cyclopropylidene) durch CuCl2-katalysierte ‘Carben-Dimerisieiung’ von 1-Bromo-1-lithiocyclopropanen

New Bi(cyclopropylidenes) by CuCl₂-Induced ‘Carbene Dimerization’ of 1-Bromo-1-lithiocycIopropanes A series of so far unknown bi(cyclopropylidenes) 5 are prepared in a simple one-pot reaction by halogenolithio exchange between 1,1-dibromocyclopropanes 1a – c as well as 1e – i and BuLi at ?95°, to give 1-bromo-1-lithiocyclopropanes 2a – c as well as 2e – i , followed by treatment with CuCl₂ at low temperature and a simple workup at room temperature (Table 1). The influence of reaction parameters on yields of 5 (Tables 2, 4, and 5) and diastereoselectivity of the reaction 2 → 5 (Table 3) are discussed. In view of an elucidation of the reaction mechanism, first kinetic experiments of the quantitative reaction 1c → 2c → 5c are reported.