摘要：

The use of titanium-based reagents to alkylidenate carbonylngroups was last comprehensively reviewed in 1993 by Pine.1 Thenmethylenation of aldehydes and ketones by these non-basic,nreactive reagents offers some advantages over other methylenationnmethods (e.g. the Wittig reaction), particularly in basesensitivensubstrates or when the carbonyl group is stericallynhindered. However, it is their ability to alkylidenate carboxylicnacid and carbonic acid derivatives that makes these reagentsnmost distinctive, and it is this aspect of their reactivity that isnreviewed here. The review covers the literature comprehensivelynfrom the beginning of 1993, and we include only selectednexamples and references to seminal papers from the periodncovered by Pine's review. First we will discuss the rangenof titanium reagents that alkylidenate carboxylic acid andncarbonic acid derivatives, the methods by which they are prepared,ntheir chemoselectivity and functional group tolerance,nand where relevant, their stereoselectivity. Only examples ofneach type of reactivity (preferably drawn from the reviewnperiod) are presented and/or cited, and we do not list everynoccurrence of a particular reaction or tolerance of a particularnfunctional group. Chemoselectivity will be discussed in terms ofnwhat functional groups are tolerated in carboxylic acid andncarbonic acid derivatives that have been alkylidenated, andnwhat functional groups are tolerated in the titanium reagentsnthemselves. The second section of the review will discuss thensynthetic strategies that have been facilitated by alkylidenationnof carboxylic acid and carbonic acid derivatives.

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