Bingel macrocyclizations

Figure 6 Representative examples of C6o bis-adducts directly produced by the Bingel macrocyclization reaction.

Figure 1.15. Bis-adducts of C6o obtained by tether-directed Bingel macrocyclization.

Scheme 7-6 General protocols for the Bingel macrocyclization reaction [25,59,60],...

Scheme 7-8 Examples of Cgg bis-adducts directly produced by the Bingel macrocyclization reaction (Scheme 7-6). For each compound, the molecular symmetry and the preparation yield are given.

The Bingel macrocyclization has been increasingly exploited in the construction of molecular building blocks for supramolecular systems. For this purpose, cis-2 bis-adducts, such as 43 with a m-xylylene tether (Scheme 7-8), have been particularly useful. Thus, bis-adducts 55 [70], a fullerene-glycodendron conjugate, and 56 [71] were shown to form stable Langmuir monolayers at the air-water interface (Scheme 7-9). 

Scheme 7-9 Examples of functional supramolecular systems containing C q cis-2 bis-adducts prepared by the Bingel macrocyclization.

Scheme 7-10 Extensions of the Bingel macrocyclization preparation of a higher adduct of Cgy [25] and use of tethered bis(jHceto esters) instead of tethered bismalonates [74]. THP=3,4,5, tetrahydro-2//-pyran-2-yl.

Since cis-3, trans-3, and trans-2 bis-adducts of 50 with identical addends are chiral as a result of inherently chiral functionalization patterns [10, 44-46], it was of interest to explore whether Bingel macrocyclizations with bismalonates bridged by non-racemic tethers would provide an enantioselective synthesis of these compounds. An overall enantioselective synthesis of optically active Cgg bis-adducts had been achieved previously by asymmetric Sharpless bis-osmylation [77] however, this sequential bis-func-tionalization lacks the regioselectivity of the Bingel macrocyclization, and therefore requires tedious regioisomer separations. 

The Bingel macrocyclization is not completely regioselective in each case [25, 59]. As an example, the use of a tether derived from l,10-phenanthroline-2,9-dimethanol yielded both e bis-adduct ( )-46 and trans-A bis-adduct 47. 

Bingel Macrocyclization Synthesis of cis-2 Bis-adduct 42 Starting from Benzene-1,2-dimethanol (Scheme 7-8) [25]... 

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