Many-Membered Carbon Rings. XXIII. Restricted Rotation in a Simple Paracyclophane^1-3

Abstract

The objective of this investigation was to demonstrate hindered rotation about single bonds in certain simple paracyolophanes. This purpose was achieved by the resolution of a suitable o-substituted paracyclophane which had ten carbon atoms in its para-bridge, as exemplified by the compound [10] paracyclophane-12-carboxylie acid. This acid was synthesized in three steps from [10]paracyclophane: [10]paracyclophane -* 12-chloromethy 1 [10]paracyclophane (73%) -[10]paracyclophane-12-carboxaldehyde (84%) -» [10]paracyclophane-12-carboxylic acid (45%). Resolution of the racemic acid, m.p. 192-193°, into its pure optical antipodes was accomplished by separation of its cinchonidine salts. The active forms of the acid, m.p.'s ca. 160°and « ± 80°, racemized slowly at room temperature in the solid, crystalline state. Illustrative of some of the difficulties encountered early in this study was the observation that succinoylation of [10] paracyclophane gave only the rearranged product 12-( -carboxypropionyl) [10-m] cyclophane, a compound unsuitable for the purpose of this study.

Analogs of Cinchona Alkaloids Incorporating a 9,9′‐Spirobifluorene Moiety

“…Each chain is composed of identical enantiomers, and the chirality of the zwitterionic molecules alternates in a regular fashion from chain to chain. Parallel to the synthesis of (k)-S, we also pursued the preparation of diastereoisomers ent-10 and ent-11 (Scheme 2) which more closely resemble quinine (1) and quinidine (2) by bearing an additional vinyl group at the quinuclidine moiety. The diastereoisomeric quinuclidine-ester precursors ent-12 and ent -13 were obtained by degradation of quinone following a procedure described by Woodward et al…”

Oxidation of Carbon–Halogen Bonds

“…36 Presumably this reaction, known by the names of its discoverers, proceeds by the displacement of the halide ion by nitronate oxygen followed by loss of the oxime (equation 15). [37][38][39][40][41] The method works well for primary allylic and benzylic chlorides and bromides. [37][38][39][40][41] The method works well for primary allylic and benzylic chlorides and bromides.…”

“…-Bender oxidation is often competitive with other methods: in equation(16)37 the Sommelet reaction gave only 20% of the aldehyde, whereas in equation(20)41 DMSO and sodium hydrogen carbonate failed to furnish any of the desired product.…”

The Acyloin Condensation as a Cyclization Method

“…A final example of the effect of a substituent on acyloin cyclization is that cited in Eq. 21 (90). If the structure of the product is that suggested by the author, it illustrates the possibility of preparing bicyclic systems by combined acyloin cyclization and transannular interaction with unsaturated substituents.…”