SYNTHESIS AND SOME REACTIONS OF A SERIES OF SKIPPED POLYACETYLENES CONTAINING TERMINAL ACETYLENE GROUPS

The synthesis and some reactions of a series of linear 1,4-polyynes containing terminal acetylene groups (Ia-e) are described. Reaction of propargyl bromide (II) with ethynylmagnesium bromide (III) in the presence of CuCl gave 1,4-pentadiyne (Ia). Rearrangement of Ia with KOBut led to 1,3-pentadiyne (IV), while treatment with Br2 furnished 1,2,4,5-tetrabromo-1,4-pentadiene (V). Oxidation of Ia with O2, CuCl and NH4Cl yielded the linear dimer (VIa) [rearranged to 2,4,6,8-decatetrayne (VIII) with KOH] and linear trimer (VIb). Hydrogenation of the crude oxidation product gave saturated hydrocarbons derived from VIa, VIb, the linear tetramer (VIc) and the cyclic tetramer (VII), but none derived from the cyclic dimer or cyclic trimer of Ia. Similarly, oxidation of Ia with Cu(OAc)2 in pyridine and subsequent hydrogenation led to saturated hydrocarbons derived from VIa and VIb, but none derived from the cyclic dimer or cyclic trimer. In order to prepare cyclodecane as a comparison compound, the cycloethylenedithioketal (X) derived from cyclodecanone was treated with Raney Ni in boiling EtOH, but the reaction led mainly to cis-cyclodecene. Treatment of 1,4-dibromo-2-butyne (XIII) with an excess of III in the presence of CuCl yielded 1,4,7-octatriyne (Ib), 1,4,7,10,13-tetradecapentayne (Id) and 1,4,7,10,13,16,19-eicosaheptayne (Ie). Rearrangement of Ib with alkaline Al2O3, or KOBut at room temp gave 2,4,6-octatriyne (XVII), while treatment with boiling ethanolic KOH or KOBut in hot ButOH led to 2-ethoxy-2-octene-4,6-diyne (XVIIIa) or 2-t-butoxy-2-octene-4,6-diyne (XVIIIc), respectively. 1,4,7,10-Undecatetrayne (Ic) was prepared from crude Ia by conversion to the bis-Grignard derivative, followed by reaction with propargyl bromide (II) in the presence of CuCl. © 1969.