Carbo-siloles, Part 2: Synthesis and Stereochemical Resolution of a Carbo-silolane Redox Equivalent

Abstract

Carbo-siloles could a priori be generated by eliminative aromatization of sila[5]pericyclyne precursors with adjacent C─OR and C─H vertices. The synthesis of tetraoxy-sila[5]pericyclyne representatives (“carbo-silolanes” 2a and 2b ) has been tackled through several [(15–n)+n] ring formation strategies. After having first attempted a [14+1] route from dichlorodiphenylsilane and a skipped pentayne ( 3 ), a [5+10] route proceeded successfully from diethynyldiphenylsilane ( 7 ) and a triynedial ( 4 ), to give the sila[5]pericyclynediol ( 2a ) as a mixture of six diastereomers in 20% yield. Sequential chromatographies afforded one pure diastereomer of 2a . DFT calculations of a model dihydroxy, dimethoxy-carbo-silolane indicate an envelope conformation of the carbo-meric five-membered ring. Methylation of the two secondary carbinol vertices of 2a afforded the corresponding tetramethoxy carbo-silolane ( 2b ) in 68% yield. Aromatization to the targeted carbo-silole by treatment with Et ₂ O·BF ₃ of 2b proved awkward.

Keywords:

• Carbo-mers
• β-diynes
• pericyclynes
• silolane
• silole
• stereochemical resolution

Acknowledgments

Dedicated to Professor Marian Mikołajczyk, CBMiM PAN in Łódź, Poland, on the occasion of his 70th birthday.

The authors wish to thank the Centre National de la Recherche Scientifique and the Ministère de l'Education Nationale, de la Recherche et de la Technologie for financial support, in particular through ACI fundings. The authors also wish to thank CALMIP (Calcul intensif en Midi-Pyrénées, Toulouse, France), IDRIS (Institut du Développement et des Ressources en Informatique Scientifique, Orsay, France), and CINES (Centre Informatique de l'Enseignement Supérieur, Montpellier, France) for computing facilities and the Ministère de l'Education Nationale de la Recherche et de la Technologie for ACI financial support. Thanks are also due to Dr. Dianne M. Fisher for her valuable comments and to Miss Katherine Black for a careful final reading.

Notes

^aFrom reference [ ¹⁷ ].

^bFrom reference [ ¹⁸ ].