title: Bullvalene trisepoxide and its stereospecific rearrangement to 2,8,12-trioxahexacyclo[8.3.0.0(3,9)0(4,6)0(5,13)0(7,11)]tridecane: two new C3-symmetrical oligocycles with propeller chirality.
abstract: Epoxidation of bullvalene (1) with a neutralized solution of Oxone gave racemic trisepoxide rac-6 in 93 % isolated yield. Its structure was examined by X-ray crystallography. The two enantiomers of 6 were separated by preparative HPLC and exhibited specific rotations of [alpha](25)(D)= +160, [alpha](25)(365)= +567 (c=0.946, CHCl(3)) for the firstly eluted and [alpha](25)(D)= -157, [alpha](25)(365)= -554 (c=0.986, CHCl3) for the secondly eluted enantiomer of 6. The geometry of (+)-6 and the absolute configuration of (-)-6 were determined by X-ray crystal structure analysis and anomalous diffraction, respectively. According to this, (-)-6 possesses (3R,5S,7S,9R,11R,13S)- and (+)-6 has (3S,5R,7R,9S,11S,13R)-configuration. Upon treatment with BF(3)Et(2)O at -78 degrees C, trisepoxide rac-6 rearranges with retention of the skeletal three-membered carbocycle to give the cage trisether rac-8, as proved by X-ray crystal structure analysis, in virtually quantitative yield. Enantiomers of rac-8 were separated by preparative HPLC and exhibited specific rotations of [alpha](25)(D)= +49, [alpha](25)(365)= +170 (c=1.01, CHCl3) (firstly eluting) and [alpha](25)(D)= -46, [alpha](25)(365)= -160 (c=1.02, CHCl(3)) (secondly eluting enantiomer). The absolute configuration of (-)-8 was determined by anomalous diffraction to be (1R,3R,7R,9R,11R,13R). DFT computations at the TD-B3 LYP/6-31+G(d,p)//B3 LYP/6-31+G(d) level of theory for (3R,5S,7S,9R,11R,13S)-6 and (1R,3R,7R,9R,11R,13R)-8 predicted specific rotations of -206.7 and -83.4, respectively. Acid-catalyzed isomerization of the enantiomerically pure (+)-6 proceeded without racemization to give exclusively (-)-8, and (-)-6 provided only (+)-8. Thus, this isomerization occurs with ring opening of the three C--O bonds in the epoxide moieties in the alpha-position relative to the three-membered carbocycle rather than in the beta-position.
authors.affiliation: Institut für Organische und Biomolekulare Chemie der Georg-August-Universität Göttingen, Tammannstrasse 2, 37077 Göttingen, Germany.
authors.forename: Shelue
authors.initials: S
authors.lastname: Liang
authors.forename: Chi-Hung
authors.initials: CH
authors.lastname: Lee
authors.forename: Sergei I
authors.initials: SI
authors.lastname: Kozhushkov
authors.forename: Dmitrii S
authors.initials: DS
authors.lastname: Yufit
authors.forename: Judith A K
authors.initials: JA
authors.lastname: Howard
authors.forename: Kathrin
authors.initials: K
authors.lastname: Meindl
authors.forename: Stephan
authors.initials: S
authors.lastname: Rühl
authors.forename: Chiyo
authors.initials: C
authors.lastname: Yamamoto
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Peter R
authors.initials: PR
authors.lastname: Schreiner
authors.forename: B Christopher
authors.initials: BC
authors.lastname: Rinderspacher
authors.forename: Armin
authors.initials: A
authors.lastname: de Meijere