Stille cyclodimerization

Since its introduction by Allred and Liebsekind in 1996 [114], copper thiophene-2-carboxylate (CuTC) has emerged as a mild and useful reagent for mediating the cross-coupling of organostannanes with vinyl iodides at room temperature. CuTC is especially effective for substrates that are not stable at high temperature. In Paterson s total synthesis of elaiolide, he enlisted a CuTC-promoted Stille cyclodimerization of vinyl iodide 131 to afford the 16-membered macrocycle 132 under very mild conditions [115]. 

In general the thermal reaction of allene gives a complex mixture of dimers, trimers, and higher oligomers including small amounts of spiro compounds (140). A highly selective dimerization to 1,2-dimethylene-cyclobutane is achieved by thermal reaction of dilute solutions Theoretically the process [2s + 2a] of allenes and related cumulenes may be facilitated by participation of the orthogonal pir-orbital in the addition 142). However, the concertedness of the cyclodimerization is still in dispute. Selective cyclotrimerization and pentamerization of allene have not... 

The dark red residue from the subhmation is still catalytically active for the cyclodimerization and cyclotetramerization of 3,3-dimethylcyclopropene. 

Retrosynthetic analysis of disorazole Cl suggested that the cyclodimerization of acid 67 would be a viable synthetic route. This was accomplished by addition of trimethylstannane 65 to a solution of dieneyl iodide 66 via a Stille coupling in the presence of a catalytic amount of Pd(CH3CN)Cl2 to give triene 67 in 76% yield [14]. 

The scheme considered is fully valid also in the case of cation-radical [2 + l]-cycloadditions. These reactions, like the corresponding thermal reactions of the [2 + 2]-cycloaddition of neutral molecules, are forbidden by the orbital symmetry conservation rules. The same calculations [95] have shown that the addition of the cation-radical of ethylene to a neutral ethylene molecule proceeds in an unconcerted and nonsynchronous fashion. Unlike the [2 + 2]-cyclodimerization of ethylene (Sect. 10.1.1), the [2 + l]-cycloaddition involves the formation of an intermediate LIII with the energy barrier calculated for this highly exothermal step being extremely low (1.3 kcal/mol by the MNDO method). A barrier lower still (1.0 kcal/mol) is expected for the step of transformation of LIII into the cation-radical of cyclobutane LIV in which the... 

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