Cage chirality of P-C cage compounds: highly diastereoselective formation of diastereomeric P5-deltacyclenes, separation of diastereomers, and removal of the chiral auxiliary.
An effective cyclic addition reaction of diastereomeric (R*)diphenyltin-3,5-di(tert-butyl)-1,2,4-triphosphole derivatives 6 a-c (R* = (-)-cis-myrtanyl (a), (-)-trans-myrtanyl (b), m-(2-bornyl-2-ene)phenyl (c) with two equivalents of tert-butylphosphaalkyne 1 leads to 1:1 mixtures of diastereomeric stannylated pentaphosphadeltacyclene derivatives 7 a-c with seven stereogenic centers in the cage unit. The (-)-cis-myrtanyl derivative 7 a could be separated into its diastereomers; destannylation of diastereomer 7 a(RR) led to the P-H cage 8 as a pure enantiomer. Circular dichroism (CD) spectroscopy of the pure diastereomer 7 a(RR) and the enantiomer 8 give evidence for identical stereoisomers of the P(5)-deltacyclene cage units and prove a strong dominance of the chiral cages over the chiral auxiliary groups with respect to their chiroptical properties. Absolute X-ray structure investigations of the majority of the compounds presented in the paper reveal the details of the stereochemistry of the asymmetric P-C cage units. In this paper we demonstrated for the first time a general preparative route to stereochemically fully defined asymmetric P-C cage compounds by separation of diastereomers and replacement of the chiral auxiliary group.
Hofmann
Martin
M
Department Chemie and Pharmazie, Erlangen Catalysis Resource Center, Universität Erlangen-Nürnberg, Egerlandstr. 1. 91058 Erlangen, Germany.
Höhn
Christine
C
Heinemann
Frank W
FW
Zenneck
Ulrich
U