General comments about catalysts, reagents, and conditions

1 General Comments about Catalysts, Reagents, and Conditions 

The intramolecular Heck cyclizations highlighted in this chapter were typically conducted with 5-20 mol% of a palladium catalyst. In few, if any, of these studies were catalyst loadings and cyclization conditions carefully optimized. As a result, we have not included catalyst loadings in the schemes in this chapter. Only recently has serious attention been directed to optimizing catalyst turnover in Heck reactions and to the development of more robust catalyst systems. It seems likely that in the future many Heck cyclizations will be accomplished with catalyst loads of 1 % or lower [76]. 

3 (—)-5,6-Dehydro-17-[10,ll-dihydro-5f/-dibenzo[fl,d]cydohepten-5-yl]-4-benzyloxy-3-methoxymorphinan (39) [12] 

To be synthetically useful, the new organometallic 3 must have a reactivity different from that of 1 in order to avoid the polymerization of the carbometallated substrate [2]. So, the carbometallation ability of 1 must be higher than that of 3, except for an intramolecular carbometallation reaction, in which case the entropy factors favor the mono-addition even if the starting organometallic and the product have similar reactivities. Since an outstanding number of additions of organometallics to carbon-carbon multiple bond have been reported and reviewed [3-5], we will focus this chapter on the more recent advances in this field (from 1991 until the present time), both from our own and from other research groups. 

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