作者:Luc Maurette、Christine Tedeschi、Emmanuelle Sermot、Michèle Soleilhavoup、Fatima Hussain、Bruno Donnadieu、Remi Chauvin
DOI:10.1016/j.tet.2004.07.052
日期:2004.10
Three different kinds of ring carbo-mers of [5]cyclitol ethers were targeted as challenging examples of functional [5]pericyclynes. Three tertiary pentaaryl-carbo-[5]cyclitol methyl ethers were synthesized through a [11 + 4] ring-closing double addition of triphenyl- and tri-p-anisyl-undecatetrayn-diides to dibenzoyl acetylene. These compounds, obtained as oily mixtures of stereoisomers, are stable and can behave as acetylenic ligands of one or two Co-2(CO)(6) units. NMR analysis reveals that the broad diasteroisomeric dispersity of a triether, is consistently reduced in the symmetrized pentaether. Three bis-secondary triaryl-carbo-[5]cyclitol methyl ethers with adjacent CH(OR) vertices were synthesized through a similar [11 + 4] ring-closing process, where the same tetrayn-diides add to both the carbaldehyde ends of the (eta(2)-OCH-C=C-CHO)Co-2(CO)(6) complex. Despite the possibility of tautomeric isomerization, the occurrence of two adjacent bis-propargylic carbinol vertices does not diminish the stability of the [5]pericyclyne framework. Finally, two bis-secondary carbo-[5]cyclitol methyl ethers with non-adjacent CH(OH) vertices were synthesized through an alternative [10 + 5] ring-closing process. The bis-secondary carbo-[5]cyclitols are regarded as isohypsic equivalents of the challenging [C,C](5)carbo-cyclopentadienyl cation. A diphenyl-hexaoxy-[5]pericyclyne with two non-adjacent secondary carbinol vertices was also prepared through a [10 + 5] ring-closing strategy: this molecule is an isohypsic equivalent of the previously calculated zwitterionic carbo-cyclopentadien one, which could be observed as a DCI/NH3-MS fragment after treatment with SnCl2/HCl. Analytical HPLC showed that the C-11 triphenyl-undecatetrayne precursor of the [11 + 4] strategy was obtained as a statistical 1:2:1 mixture of the three possible diastereoisomers. Semi-preparative HPLC allowed for the resolution of this mixture. The pure major diastereoisomer was employed to prepare a partly resolved sample of pentamethoxy-pentaphenyl-[5]pericyclyne. Analytical HPLC showed that the latter corresponds to the statistical distribution of the expected three residual diastereoisomers. Semi-preparative HPLC finally afforded samples of diastereoisomerically pure pentamethoxy[5]pericyclyne as crystalline solids. (C) 2004 Elsevier Ltd. All rights reserved.