Enolate compounds natural product synthesis applications

Lactones are normally stable compounds, which have found ample application as synthetic intermediates, and, quite recently, have been detected as the central structural unit in physiologically active natural products like obaflorin (123) and lipstatin (124). Characteristic applications of 3-lactones in synthesis are the stereospecific CO2 elimination to form di- and tri-substituted alkenes (e.g. from 125 equation 40) or Grignard addition to the carbonyl group e.g. equation 41). Particularly useful is the formation of 3-lactone enolates (126), which react with a variety of electrophiles (EX) wiA high stereocontrol (equation 42). Organocuprates may be used in chain elongations to form 3-branched carboxylic acids (equation 43). ... 

Dutch elm disease is a fungal disease, carried by elm bark beetles, which devastated the elm populations of many parts of the world in the 1970s. The beetles assemble at a suitable elm tree on the call of a pheromone containing, among compounds derived from the tree, one charactacteristic of the beetle itself, multistriatin 48. The stereochemistry of this compound was deduced by the synthesis of the various possible isomers as so little natural product was available.8 We shall use three of these syntheses to illustrate the application of aza-enolates to alkylation reactions. 

Numerous applications of titanium enolate aldol reactions have been reported for the synthesis of natural products and bioactive compounds of pharmaceutical interest. These syntheses were performed by utilizing the titanium enolate methods described above as key steps. There are many transformations that simply cannot be achieved by use of conventional aldol chemistry. Furthermore, the use of inexpensive titanium reagents, operational simplicity, and functional group tolerance make this chemistry very attractive in synthesis. The following applications in synthesis further exemplify the increasing importance of titanium aldol chemistry. 

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