title: A multistep single-crystal-to-single-crystal bromodiacetylene dimerization.
abstract: Packing constraints and precise placement of functional groups are the reason that organic molecules in the crystalline state often display unusual physical or chemical properties not observed in solution. Here we report a single-crystal-to-single-crystal dimerization of a bromodiacetylene that involves unusually large atom displacements as well as the cleavage and formation of several bonds. Density functional theory computations support a mechanism in which the dimerization is initiated by a [2 + 1] photocycloaddition favoured by the nature of carbon-carbon short contacts in the crystal structure. The reaction proceeded up to the theoretical degree of conversion without loss of crystallinity, and it was also performed on a preparative scale with good yield. Moreover, it represents the first synthetic pathway to (E)-1,2-dibromo-1,2-diethynylethenes, which could serve as synthetic intermediates for the preparation of molecular carbon scaffolds. Our findings both extend the scope of single-crystal-to-single-crystal reactions and highlight their potential as a synthetic tool for complex transformations.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Institute of Materials, Laboratory of Macromolecular and Organic Materials, EPFL STI IMX LMOM, Building MXG 037, Station 12, CH-1015 Lausanne, Switzerland.
authors.forename: Tobias N
authors.initials: TN
authors.lastname: Hoheisel
authors.forename: Stephen
authors.initials: S
authors.lastname: Schrettl
authors.forename: Roman
authors.initials: R
authors.lastname: Marty
authors.forename: Tanya K
authors.initials: TK
authors.lastname: Todorova
authors.forename: Clémence
authors.initials: C
authors.lastname: Corminboeuf
authors.forename: Andrzej
authors.initials: A
authors.lastname: Sienkiewicz
authors.forename: Rosario
authors.initials: R
authors.lastname: Scopelliti
authors.forename: W Bernd
authors.initials: WB
authors.lastname: Schweizer
authors.forename: Holger
authors.initials: H
authors.lastname: Frauenrath