Chemie angeregter zustände. I. Mitt. Die richtung der photocyclisierung naphthalinsubstituierter äthylene

Carbohelicenes and heterohelicenes

“…The asymmetric synthesis of [10] via [4+3+ 1) has a very low optical yield (0.03 %). No asymmetric synthesis is observed with (4+1+4) and (4+3+2) for [11], (4+3+3) for [12] and (4+3+4) for [13] helicene. There is no clear explanation for this behaviour 6a).…”

“…A more simple way to determine the preferred route for the photocyclization of a diarylethylene is to count the number of benzene rings in the DHP's. From Scheme 3 as an example, it can be deduced that I1 (1-naphthyl (n) + 1-benzene (b)) is preferred to 12 (2b), to 13 (In) and to 14 (lb).…”

Synthesis and X-ray Analysis of New [5]Helicenes – HMO Calculations on the Photocyclization of the Stilbene Precursors

“…That, in conclusion, is the theoretical background for (ΣF* r,s ) (F r ϭ √3 Ϫ ΣP r , P ϭ bond order). [4] Numerous examples lead to the conclusion that photocyclization only the highly diluted solutions required in the photoreaction.…”

“…The reaction mixture was poured into H 2 O (10 phosphonium bromide (13) yielded 0.5 g (41%) of a yellow solid mL), the aqueous mixture extracted with ether (3 ϫ 2 mL), the after extraction with toluene and crystallization from toluene, mp combined organic phases were washed with H 2 O (4 ϫ 2 mL), brine 245°C. Ϫ Spectroscopic data refer to the all-trans isomer: IR (2 mL), and dried with MgSO 4 …”

“…Scholz, Mühlstedt, and Dietz rationalized this unique reactivity pattern in terms of the highest free valence (F* r,s ) or the lowest localization energy (L* r,s ) in the excited state, respectively. [4] Later Laarhoven and coworkers deduced some rules from a variety of examples which may be summarized as follows: [5] (i) Photocyclizations only take place if ΣF* r,s > 1, and (ii) only one product is formed if ∆Σ F* r,s > 0.1. Indicated by these rules, the exclusive formation of [5]helicene C from B is obviously subject to the condition of a low concentration of the startScheme 1.…”