Formation of Cyclic Oligomers by Cycloaddition

Several cyclic oligomers 1-5 are prepared from butadiene using transition metal catalysts. The preparation of 1,5-cyclooctadiene (3 1,5-COD) by a catalyst prepared from Ni(CO)4 and phosphine is the first report on cyclooligomerzation of butadiene [1], However, the activity of this catalyst is low due to strong coordination of CO. Catalyst prepared from TiCU and EtjAl has higher catalytic activity for the formation of 1,5-COD and 1,5,9-cyclododecatriene (1,5,9-CDT 4). Also Ni(0) catalysts are active for the preparation of COD and CDT. In addition to COD and CDT, the cyclic 

Cyclization of butadiene catalysed by Ni(0) catalysts proceeds via 7r-allylnickel complexes. At first, the metallacyclic bis-7i-allylnickel complex 6, in which Ni is bivalent, is formed by oxidative cyclization. The bis-7r-allyl complex 6 may also be represented by cr-allyl structures 7, 8 and 9. Reductive elimination of 7, 8 and 9 produces the cyclic dimers 1, 2 and 3 by [2+2], [2+4] and [4+4] cycloadditions. Selectivity for 1, 2 and 3 is controlled by phosphine ligands. The catalyst made of a 1 1 ratio of Ni and a phosphine ligand affords the cyclic dimers 1, 2 and 3. In particular, 1 and 3 are obtained selectively by using the bulky phosphite 11. 1,2-Divinylcyclobutane (1) can be isolated only at a low temperature, because it undergoes facile Cope rearrangement to form 1,5-COD on warming. Use of tricyclohexylpho-sphine produces 4-vinylcyclohexene (2) with high selectivity. 

Avery active form of Ni(0) is generated from bis-7r-allylnickel (12) and Ni(cod)2 (13) in the absence of phosphine ligand, and is often called naked Ni(0). Three butadienes coordinate to naked Ni(0) and the 18-electron trimeric complex 10 is 

9-CDT is produced commercially and used for production of 12-nylon. Interesting synthetic reactions have been reported based on the modification of CDT-and COD-forming reactions. Di- and tetraazacyclododecatrienes 20 and 21 were prepared by cooligomerization of the diazadiene 19 and butadiene [5,6]. 

Interesting synthetic applications of the [4+4] and [4+4+4] cycloadditions are reported. A novel, short-step synthetic method of muscone (24) has been developed using complex 10 as a starting compound [7]. Insertion of allene to the Ni-carbon bond in 10 at low temperature gives the bis-7r-allylnickel 22. Then isonitrile is inserted to 22. When the reaction mixture is warmed, the 15-membered cyclic compound 23 is formed by reductive elimination, and conversion of 23 to muscone (24) is achieved by hydrolysis and subsequent hydrogenation in 43 % overall yield. 

---