Rh(1)-Catalysed Rearrangements of 3,4-Diacyloxy-l,S-hexadiy nes;Synthesis of (E)-4-Acyloxymethyliden-2-cyclopenten-l-ones SummaryThe 3,4-diacyloxy-l,5-hexadiynes 3, 6 and 8 which were synthesized according to a known, slightly modified procedure react with [Rh(CO),Cl], at 100" in chloroform with formation of the (E)-4-acyloxymethyliden-2-cyclopenten-1-ones 4, 7 and 9 (Schemes 2, 3 and 4), respectively. DL-and meso-3 as well as trans-and cis-8, give the same (E)-isomers 4 and 9, respectively. 3,4-Diacetoxy-3,4-dimethyl-1,6-diphenyl-I, 5-hexadiyne (10) produces with the same catalyst 2,6-diacetoxy-3,4-dimethyl-l,6-diphenylfulvene (11) (Scheme 5). A mechanism for the formation of the cyclopentenones is proposed in Scheme 6.