OLIGO(CYCLOHEXYLIDENES) - PARENT COMPOUNDS AND END-FUNCTIONALIZED DERIVATIVES

Parent oligo(cyclohexylidenes) 1(n) (n = 1-4) were synthesized using a modified Barton-Kellogg olefin synthesis. Surprisingly, the crude com pounds 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)d(4)d(4) and 1(2)-d( 8), their formation can be attributed to scrambling of the intermediat e azines. With increasing n, a marked decrease in solubility as well a s an increase in thermal stability was found. Powder diffraction measu rements indicate that the parent compounds 1(n), irrespective of n, pa ck in a similar fashion in the solid state. The theoretically (MMX, AM 1, and ab initio) predicted rodlike structure of the oligo(cyclohexyli denes) was confirmed by single-crystal X-ray structures of 1(1) and th ree derivatives (12(1), 13(1), and 30(2)). In line with the powder dif fraction data in the series 1(n), a similar packing motif was found fo r the derivatives. To circumvent side product formation due to azine s crambling, a different synthetic approach was used for the preparation of end-functionalized oligo(cyclohexylidenes), i.e. decarboxylation a nd dehydration of beta-hydroxy acids.