4,7,11-triheterotrishomocubanes - Propeller-shaped highly symmetrical chiral molecules derived

Epoxidation of barrelene (3) with a neutralized solution of Oxone (R) gave the barrelene trisepoxide 6 in 82% isolated yield, while lead tetraacetate promoted aziridination of 3 with two equiv. of N-aminophthalimide gave a mixture of mono-7 and bis(aziridine) endo,exo-B, which were isolated in 67 and 8% yield, respectively. Fourfold repetition of this aziridination gave the bis(aziridines) exo,exo- and endo,exo8 along with the trisaziridine 9 in 21, 8 and 19% yield, respectively. Epoxidation of 7 and endo,exo-8 with buffered m-chloroperbenzoic acid furnished the dioxaazatrishomobarrelene 10 and oxadiazatrishomobarrelene 11 in 36 and 62% yield, respectively. The structures of triheteratrishomobarrelenes 6 and 9 were established by X-ray crystallography. Upon treatment with (BF3Et2O)-Et-. at -20 degrees C (for 6) or with the strongly acidic ion exchange resin Amberlyst 15 at ambient or elevated temperatures (for 9-11), these triheteratrishomobarrelenes rearrange to give the triheteratrishomocubanes rac-12 to rac-15, as proved by X-ray crystal structure analysis of rac-13, in 75-100% yield. The enantiomeric pairs of trioxa-12 and triazatrishomocubane 13 were separated by preparative HPLC on a chiral column. 12 exhibited specific rotations of [alpha](D)(25) = +196 and [alpha](365)(25) = +652 (c = 0.497, CHCl3) for the firstly eluted and [alpha](D)(25) = -173 and [alpha](365)(25) = -608 (c = 0.503, CHCl3) for the secondly eluted enantiomer; 13 had [alpha](D)(25) = +30 and [alpha](435)(25) CHCl3) for the firstly as well as [alpha](435)(25) =-28 and [alpha](435)(25) = -475 (c = 0.501, CHCW for the secondly eluted enantiomer. The geometry of rac-13 and the absolute configurations of (+12 and (+)-13 were determined by X-ray crystal structure analyses. According to this, (+12 and (+)-13 possess the same (1 R,3R,5R,6R,8R, 10R)-configuration. The absolute configuration of the former was also confirmed by DFT computations at the TD-B3LYP/6-31+G(d,p)//B3LYP/6-31+G(d) level of theory; the computed specific rotation for (+ 12 was -178. Computations for the elusive (all-R)-triazatrishomocubane (all-R)-13-H without phthalimidyl substituents on the nitrogen atoms disclosed that the sign of rotation is the same for the parent (all-R)-13-H and (all-R)-trioxatrishomocubane (all-R)-12 with the same absolute configuration.