Wittig rearrangements synthetic applications

Reviews have appeared on the use of the Wittig reaction in industrial practice, the Claisen rearrangement, synthetic applications of the retro-Diels-Alder reaction, organo-palladium intermediates for the alkylation and arylation of olefins, the Prins reaction to give 1,3-dienes, and intramolecular [4 + 2] (Diels-Alder) and [3 + 2] cycloadditions.An interesting discussion of the regiospecificity of the Diels-Alder reaction in terms of frontier orbital overlap favours the Woodward-Katz concept. Useful alkyne and polyene coupling reactions are described in reviews on the chemistry of vitamin the synthesis of insect sex... 

The [1,4]-Wittig rearrangement is potentially useful not only for the carbon-carbon bond formation but also for enolate formation. However, synthetic applications have been rather limited, because of the low yields and restricted range of substrates. Schlosser s group have developed a practical approach to aldehydes based on a [1,4]-rearrangement/ enolate trapping sequence. In contrast, standard aqueous workup gave poor yield of aldehyde. This protocol was employed as the key step in a synthesis of pheromone (102) from 99 via 100 and 101 (equation 56f. ... 

Review articles have addressed advances in photochemical generation and reactions of carbanions,165 the [l,2]-WMg rearrangement stereochemistry and synthetic application,167 and the aza-Wittig rearrangement.168... 

Both intermolecular and intramolecular additions of carbon radicals to alkenes and alkynes continue to be a widely investigated method for carbon-carbon bond formation and has been the subject of a number of review articles. In particular, the inter- and intra-molecular additions of vinyl, heteroatomic and metal-centred radicals to alkynes have been reported and also the factors which influence the addition reactions of carbon radicals to unsaturated carbon-carbon bonds. The stereochemical outcome of such additions continues to attract interest. The generation and use of alkoxy radicals in both asymmetric cyclizations and skeletal rearrangements has been reviewed and the use of fi ee radical reactions in the stereoselective synthesis of a-amino acid derivatives has appeared in two reports." The stereochemical features and synthetic potential of the [1,2]-Wittig rearrangement has also been reviewed. In addition, a review of some recent applications of free radical chain reactions in organic and polymer synthesis has appeared. The effect of solvent upon the reactions of neutral fi ee radicals has also recently been reviewed. ... 

In the first purely synthetic application of the reaction, Schreiber employed the 1,2-Wittig rearrangement to synthesize 1,3-diol monoethers (equation 15). The syn products (56) were obtained in 14—32% yield with 90-95% diastereoselectivity (Table 3). The 1,4-product (57) was found to predominate at low temperature, whereas at 0 °C the 1,2-product was favored but the absolute yield did not increase. 

Since then, the [2,3]-Wittig rearrangement has been utilized in numerous synthetic applications. Highly stereoselective variants, and hetero [2,3]-Wittig rearrangements have also been discovered, and several excellent reviews have been published. ... 

Another protocol represents the first example of a C-glycoside synthesis based on a [1,4]-Wittig rearrangement (eq 37). Moreover, interception of the intermediate lithium enolate with an external electrophile is achieved. In addition, the application of this synthetic strategy for the synthesis of zaragozic acid A is demonstrated. ... 

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