The carbonylation of the substituted 2-butyne-1,4-diols, RArC(OH)equivalent to(OH)ArR (Ar, 2,5-dimethylthienyl; R, alkyl) was studied by using Pd(OAc)(2)/I-2 as the catalyst in benzene under pressure. The diols bearing methyl or isopropyl group as the alkyl substituent gave photochromic fulgide (4a or 4b). On the other hand, the carbonylation of the diol bearing bulky t-butyl group did not afford the corresponding fulgide but lactone 5, together with butatriene 6. (C) 2002 Elsevier Science B.V. All rights reserved.