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1, x ‐Elimination Reactions: Extending the Limits of a Classical Organic Reaction
Author(s) -
Werner Christian,
Hopf Henning,
Dix Ina,
Bubenitschek Peter,
Jones Peter G.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700827
Subject(s) - chemistry , reagent , dimer , elimination reaction , acetonitrile , enediyne , medicinal chemistry , yield (engineering) , solvent , stereochemistry , organic chemistry , materials science , metallurgy
α,ω‐Dibromo derivatives in which the two terminal carbon atom are separated by an unsaturated spacer unit (“π spacer”) undergo 1, x ‐elimination reactions (with x = 6, 8, 10, and 14), using Mori's reagent ( n Bu 3 SnSiMe 3 /CsF). The resulting cumulenic intermediates cyclodimerize in a subsequent step yielding novel macrocyclic acetylenic and bridged aromatic compounds (cyclophanes). Thus 1,6‐eliminations were carried out with dibromide 17 to yield 1,3,7,9‐cyclododecatetrayne ( 20 ) and with benzylbromide 24 to provide cyclophanes 26 and 27 . By 1,8‐eliminations the 16‐membered macrocycle 33 could be prepared from enediyne 31 , the benzannelated 1,5‐cyclooctadiyne 41 from dibromide 38 , and a mixture of cyclophanes 45 and 46 from the precursor 43 . 1,10‐Eliminations were carried out successfully with dibromides 47 , 50 , and 53 yielding the corresponding unsaturated cyclophanes (“cyclophynes”) 49 , 52 , and 55 . The influence of the solvent on the cyclodimerization 47 → 49 was investigated, with acetonitrile providing the highest yields. The heterophanes 59 a and b were obtained by 1,10‐elimination of the precursor dibromides 57 a and b , and in an elimination experiment involving a 1:1 mixture of the dibromides 50 and 57 b the “mixed dimer” 60 was isolated, besides the homodimers 52 and 59 b . The method reached its limits with the 1,14‐elimination of 68 , 70 , and 74 providing the cyclophanes 69 , 71 , and 75 in varying amounts. Two final debrominations with 76 and 77 , which in principle could undergo 1,16‐ and 1,20‐eliminations reactions, respectively, failed. The structures of the new cyclophanes 49 , 50 , 59 a , and 59 b were established by X‐ray structural analysis; all other structure assignments rest on the usual spectroscopic and analytical data.