Helvetica Chimica Acta

doi: 10.1002/hlca.19770600501pmid: N/A

Schlecker, Rainer; Seebach, Dieter

doi: 10.1002/hlca.19770600502pmid: N/A

Of the isoelectronic 6‐electron systems 1a, 1b, 1c (Table 1) the deprotonated amides 2 might be useful derivatives for amine acidification (eq. (1)) if the carbonyl group is sterically protected as shown in 3. The tetrasubstituted succinimides 4, 5, 7, 8 and 9 (diacylamines) undergo the reactions (b), (c) and (d) of Scheme 1 with various bases. Besides deprotonation, the ‘self addition’ to give dimers 4b, 5b, 8b and 9b is the most prominent transformation (Table 2). Only in 9 is the steric hindrance to carbonyl addition large enough to get the lithiomethyl‐succinimides 9c in 80% yield (sec.BuLi/THF/HMPT/‐100°) as evidenced by derivatization with alkyl halides, aldehyde, ketones, methyl benzoate, and chloro trimethylsilane (→9d ‐ 9j, Table 3). The possible structures and bonding descriptions for 9c which ‘decomposes’ above −40° are discussed; the acidity of the precursor 9 is shown by equilibration studies to be comparable with that of diphenylmethane.

Tissot, Paul; Margaretha, Paul

doi: 10.1002/hlca.19770600503pmid: N/A

The electrochemical reduction of the cyclohex‐2‐enones 1a–1e (mercury cathode, CH3CN, Bu4NBF4) was studied by means of cyclic voltammetry, d.c. polarography, coulometry and chemical product analysis. Compounds 1a–1c give a mixture of the hydrodimers 4 and 5 via formation of the radical anion 2 by an irreversible one electron transfer, followed by protonation and dimerization of the allylic radical 3. The 6‐halocyclohex‐2‐enones 1d and 1e exhibit two distinct reduction waves. The first corresponds to an irreversible two electron transfer with formation of the halide anion and the enolate anion 6 which gives 1b by protonation. The second wave corresponds to a quasi‐reversible one electron transfer to 6 to afford the radical dianion 7 (Scheme 2).

Kramis, Jost; Hansen, Hans‐Jürgen

doi: 10.1002/hlca.19770600504pmid: N/A

On the Base‐Catalysed H/D‐Exchange of the Acetylenic Hydrogen Atom in Aromatic Alkynyl Compounds

Niemeyer, Hermann M.

doi: 10.1002/hlca.19770600505pmid: N/A

CNDO/2, MINDO/3 and ab initio molecular orbital calculations are used in a study of conformational isomerism, protonation site and mechanism of protonation of the title compounds.

Ohloff, Günther; Giersch, Wolfgang

doi: 10.1002/hlca.19770600506pmid: N/A

Verbenone 1 or 2 is converted in three steps to ipsdienol 9 or 10 respectively. The diastereoisomeric 2(10)‐pinen‐4‐ols 6 and 7 (or 5 and 8), wich have identical chirality at the carbon atoms bearing OH groups, afford ipsdienol 10 (or 9 respectively) with the same optical purity as the starting material.

Schwotzer, Willi; Von Philipsborn, Wolfgang

doi: 10.1002/hlca.19770600507pmid: N/A

15N‐Chemical shifts of 32 enamines, 11 enaminoketones and 28 closely related amines have been determined with the isotope in natural abundance. In order to eliminate substituent effects, differential chemical shifts Δδ(N) are defined as δN(amine)‐δN(enamine). This parameter is shown to correlate well with the free enthalpy of activation ΔG# for restricted rotation about the NC(α) bond in enamines with extended conjugation. Δδ(N) values of substituted anilinostyrenes correlate also with 13C‐chemical shifts of the β‐carbon in the enamine system and with Hammett σ‐constants of the aniline substituents. The experimental results suggest that differential 15N shifts are a useful probe to study n, π‐interaction in enamines.

Scartazzini, Riccardo

doi: 10.1002/hlca.19770600508pmid: 893122

New β‐lactam antibiotics. Functionalisation of 3‐hydroxy‐3‐cephem‐4‐carboxylic esters through the Wittig reaction

Breitenstein, Werner; Tamm, Christoph

doi: 10.1002/hlca.19770600509pmid: N/A

A new metabolite, verrucarin K (C27H34O8) has been isolated from a strain of Myrothecium verrucaria (ALBERTINI et SCHWEINITZ) DITMAR ex FRIES. On the basis of spectral and chemical evidence structure 1 was assigned to the new compound. Base‐catalysed hydrolysis yielded verrucarinolactone (5), E,Z‐muconic acid (6) and trichotheca‐9, 12‐diene‐4,15‐diol (3). The implications of 1 in the trichothecane biosynthesis are discussed.

Brook, Peter R.; Jonathan Duke, A.; Glenville Griffiths, J.; Roberts, Stanley M.; Rey, Max; Dreiding, André S.

doi: 10.1002/hlca.19770600510pmid: N/A

Synthese und Umlagerung von 7‐Halo‐bicyclo[3.2.0]hept‐2‐en‐6‐olen