Oligo(cyclohexylidenes): Parent Compounds and End-Functionalized Derivatives

Article abstract of DOI:10.1021/jo00119a014

Parent oligo(cyclohexylidenes) 1(n) (n = 1-4) were synthesized using a modified Barton-Kellogg olefin synthesis.Surprisingly, the crude compounds 1(2) and 1(4) contained small amounts of the 1(n-1) and 1(n+1) homologues.As evidenced by a close examination of mass spectral data of selectively deuterated tercyclohexylidenes 1(2)-d4d4 and 1(2)-d8, their formation can be attributed to scrambling of the intermediate azines.With increasing n, a marked decrease in solubility as well as an increase in thermal stability was found.Powder diffraction measurements indicate that the parent compounds 1(n), irrespective of n, pack in a similar fashion in the solid state.The theoretically (MMX, AM1, and ab initio) predicted rodlike structure of the oligo(cyclohexylidenes) was confirmed by single-crystal X-ray structures of 1(1) and three derivatives (12(1), 13(1), and 30(2)).In line with the powder diffraction data in the series 1(n), a similar packing motif was found for the derivatives.To circumvent side product formation due to azine scrambling, a different synthetic approach was used for the preparation of end-functionalized oligo(cyclohexylidenes), i.e. decarboxylation and dehydration of β-hydroxy acids.