~~It is shown that dimethyl 7-isopropyl-5, IO-dimethylheptalene-1,2-dicarboxylate (1) and dimethyl 5,6,8,10-tetramethylheptalene-l,2-dicarboxylate (2) can be resolved via the corresponding mono-acids and with the aid of optically active primary or secondary amines such as I-phenylethylamine or ephedrine into the (-)-(P)-and (+)-(M)-enantiomeres, respectively. Characteristic for the (P)-chirality of the heptalene n-skeleton with C, or pseudo-C, symmetry are two (-)-CE's at the long wavelength region (450-300 nm) followed by at least one intense (+)-CE at wavelengths about or below 300 nm. The absolute configuration of the heptalenes was correlated with the well-established absolute configuration of (+)-(R)-and (-)-(S)-l -phenylethanol.

The reaction of highly alkylated azulenes with dimethyl acetylenedicarboxylate (ADM) in decalin or tetralin at 180-200" yields, beside the expected heptalene-and azulene-l,2-dicarboxylates, tetracyclic compounds of type 'anti'-V and tricyclic compounds of type E (cf Schemes 2-4 and 8-11). The compounds of type 'anti'-V represent Diels-Alder adducts of the primary tricyclic intermediates A with ADM. In some cases, the tricyclic compounds of type E also underwent a consecutive Diels-Alder reaction with ADM to yield the tetracyclic compounds of type 'anti'-or 'syn'-VI (cf. Schemes 2 and 8-11). The tricyclic compounds of type E, namely 4 and 8, reversibly rearrange via [ 1,5]-C shifts to isomeric tricyclic structures (cf. 18 and 19, respectively, in Scheme 6) already at temperatures > 50". Photochemically 4 rearranges to a corresponding tetracyclic compound 20 via a di-n -methane reaction. The observed heptalene-and azulene-l,2-dicarboxylates as well as the tetracyclic compounds of type 'anti'-V are formed from the primary tricyclic intermediates A via rearrangement (+ heptalenedicarboxylates), retro-Diels-Alder reaction (+azulenedicarboxylates), and Diels-Alder reaction with ADM. The different reaction channels of A are dependent on the substituents. However, the main reaction channel of A is its retro-Diels-Alder reaction to the starting materials (azulene and ADM). The highly reversible Diels-Alder reaction of ADM to the five-membered ring of the azulenes is HOMO(azulene)/LUMO(ADM)-controlled, in contrast to the at 200" irreversible ADM addition to the seven-membered ring of the azulenes to yield the Diels-Alder products of type E. This competing reaction must occur on grounds of orbital-symmetry conservation under SHOMO(azulene)/LUMO(ADM) control (cf . Several X-ray diffraction analyses of the products were performed (cf. Chap. 4 . 1 ) . Introduction. -It has been well established over the past years by Hafner et al. (cf.[I] [2]) as well as by our own work (cf [3][4][5]) that the thermal reaction of azulenes with dimethyl acetylenedicarboxylate (ADM) in apolar solvents such as tetralin or decalin at 180-200" represents the shortest and most versatile access to the heptalene skeleton, in particular, to heptalene-1,2-dicarboxylates. In addition, it has been shown that heptalene-1,2-dicarboxylates and their derivatives undergo thermal [2] [5-71 (see also [8] [9]) and photochemical double-bond shifts (DBS) [5] [6] as well as thermal a-skeletal rearrangements [lo] [11], and that heptalenes with substituents in theperi-positions can be resolved into their antipodes [2] [4] [7] [12]. In contrast, very little is known on the primary steps in the thermal reaction of azulenes with ADM. It has been postulated by Hafner et al. [ 13 [2] that azulenes and ADM yield as a first intermediate a zwitterionic species (ZI; CJ Scheme I) from which all observed thermal products (1 to IV) are derived.

It is shown that dimethyl 5,6,8,1O-tetramethyl-(3) and 8-(tert-butyl)-5,6,lO-trimethylheptalene-1,2-dicarboxylate (S), and their derivatives rearrange reversibly on irradiation or on heating to yield the corresponding 1,6,8,10-tetramethyI-(4) and 8-(tert-butyl)-1,6,lO-trimethylheptalene-1,2-dicarboxylate (6), and their derivatives by double-bond shift (n-skeletal rearrangement) via a transition state with D, symmetry as the highest possible one. This follows from the fact that (-)-(P)-3 is photochemically as well as thermally rearranged to give (-)-(P)-4 i.e. the n-skeletal rearrangement occurs with retention of configuration of the heptalene skeleton and without loss of optical purity.

The chiral structure of heptalenc is characterised, for a given configuration, by helicities, which are opposite in the direction (.x) of the central C(Sa)-C(lOu) bond and in the direction (J) of a line perpendicular to it, passing through the C(3)-and C(R)-atoms. These two helicities can be experimentally established and differentiated by the handedness of the cholesteric mesophases induced in a biphenyl-type liquid crystal (LC) by chiral heptalenes with substiliients favouring the x or J orientation along the nematic director of the LC.

Yeast reduction of ethyl acetoacetate: ( S )‐( + )‐ethyl 3‐hydroxybutanoate reactant: 20.0 g (0.154 mol) of ethyl acetoacetate product: (S)‐( + )‐ethyl 3‐hydroxybutanoate reactant: ethyl (S)‐( + )‐3‐(3′,5′‐dinitrobenzoyloxy)butanoate product: methyl 3‐hydroxybutanoate byproduct: (R‐)‐( − )‐Ethyl 3‐hydroxybutanoate