Synthesis and stereochemical resolution of functional [5]pericyclynes Luc Maurette, Christine Tedeschi, Emmanuelle Sermot, Miche `le Soleilhavoup, Fatima Hussain, Bruno Donnadieu and Remi Chauvin * Laboratoire de Chimie de Coordination, 205 Route de Narbonne 31077 Cedex 4, Toulouse, France Received 27 April 2004; revised 25 June 2004; accepted 14 July 2004 Available online 15 September 2004 Abstract—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 [11C4] ring-closing double addition of triphenyl- and tri-p-anisyl-undecatetrayn-diides to dibenzoylacetylene. 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 [11C4] ring-closing process, where the same tetrayn-diides add to both the carbaldehyde ends of the (h 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 [10C5] 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 [10C5] ring-closing strategy: this molecule is an isohypsic equivalent of the previously calculated zwitterionic carbo-cyclopentadienone, which could be observed as a DCI/NH 3 -MS fragment after treatment with SnCl 2 /HCl. Analytical HPLC showed that the C 11 triphenyl-undecatetrayne precursor of the [11C4] 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. q 2004 Elsevier Ltd. All rights reserved. 1. Introduction In the general field of carbon-rich molecules, 1 we have been interested for some time in a carbon ‘enrichment’ process which could preserve some memory of its poorer parent molecule. Meeting the field of polyacetylenic chemistry, 2 it consists in the linear insertion of two sp carbon atoms into each bond of the parent Lewis skeleton. It is readily checked from basic VSEPR and mesomerism that the resulting ‘carbo-mer’ structure preserves essential features of the parent model (connectivity, shape, symmetry, p-resonance, CIP configurations of stereogenic centers), while it has experienced a three-fold size expansion. 3 Focusing on cyclic hydrocarbons, carbo-mers of unsaturated rings such as annulenes 4 and radialenes, 5 were theoretically compared in terms of aromaticity. In a more subtle manner, ring carbo-mers of saturated cycloalkanes were theoretically compared in terms of homo-aromaticity. 6 These ‘carbo- cycloalkanes’ are actually [N]pericyclynes, a generic term coined by Scott et al. in 1983 as they reported the synthesis of the first representative, decamethyl[5]pericyclyne (Scheme 1). 7 An octamethyl analogue was later reported. 8 The fascinating structure and stability of these rigid p- electron-rich 15-membered rings then attracted a consider- able theoretical interest. 9,2,4,6 Nevertheless, an open ques- tion is whether the stability of [5]pericyclynes is compatible with functionalities at the sp 3 vertices. Hexaoxy-[6]pericy- clynes, 10a and expanded peroxy-pericyclynes (made with butadiyne edges and ketal vertices) have been described. 10b To the best of our knowledge however, beside mentions of few peralkyl-monohydroxy-[5]periclynes, 11 no functional simple [5]pericyclyne was hitherto described in the literature. We focus here on the synthesis of pentaoxy- [5]pericyclynes, which can be alternatively regarded as ‘carbo-[5]cyclitol’ derivatives (Scheme 1). Beyond the 0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2004.07.052 Tetrahedron 60 (2004) 10077–10098 Keywords: Carbo-mers; Pericyclynes; Cyclization reactions; Acetylenedi- carbaldehyde; Diastereoisomeric resolution. * Corresponding author. Tel.: C335-61-33-31-13; fax: C335-61-55-30- 03; e-mail: chauvin@lcc-toulouse.fr