Cyclopropenes trimerization

Cycloaddition of cyclopropenes is catalyzed by transition metal complexes. 1-Methylcyclopropene 118 undergoes a facile PdCl2(PhCN)2-catalyzed cyclodimerization to dimethyltricyclo[3.1.0.02,4]hexanes 119. In contrast, cyclo-trimerization of 3,3-dimethylcyclopropene 120 occurs in the presence of a catalytic amount of Pd(PPh3)4 to give hexamethyl-frans-ff-trishomobenzene 121... 

Cyclopropenes react very easily with 1,2,4-triazines. The azanorcaradienes (378), or their valence tautomers, the 4//-azepines (379), were isolated via the tricyclic intermediates (380) and loss of nitrogen. The equilibrium between (378) and (379) depends on the substituents. The 4//-azepines rearrange to the 3//-compounds (381) (80TL595, 72JA2770). The parent 1,2,4-triazine (1) also reacts with cyclopropene, but the product seems to be a trimer of the azanorcaradiene, of uncertain structure (70UP21901). 

As further illustrated in Scheme 2, the 1-methyl- and 1,3,3-trimethylcyclopropene are rapidly metallated with organolithium reagents in ether to afford stable solutions of the 1-lithiocyclopropenes (18) In comparison, solutions of the metallocyclopropenes (16) are significantly less stable and even at — 40°C are observed to degrade slowly to a mixture of dimeric and trimeric products apparently formed by nucleophilic addition of 16 to the highly reactive cyclopropene n system L Alkylation of 18 (R=H or Me) with methyl iodide produced 1,2-dimethyl- and 1,2,3,3-tetramethylcyclopropene . The trimethyl derivative 18 (R = Me) has also been carbonated and acylated to afford the corresponding 2,3,3-trimethylcyclopropene carboxylic acid, methyl ketone and carboxaldehyde. 

Tetrakis(triphenylphosphine)palladium(0) Reactions with cyclopropenes ran -a-Trishomobenzenes by trimerization... 

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