Aldol Wittig rearrangement

This [1,4]-Wittig rearrangement system is applicable to the sequential [l,4]-rearrange-ment/aldol reaction which provides -hydroxy ketones with moderate diastereoselectivity (Table 4). 

Other Uses. Reagent 1 has been used for enantioselec-tive enolborination, albeit with poor (1.1 1) selectivity. Similar bis-sulfonamide-derived boron Lewis acids have been used for aldol additions, "" ester-Mannich reactions, Diels-Alder reactions, Ireland-Claisen reactions, and [2,3]-Wittig rearrangements. Similar bis-sulfonamide-derived aluminum Lewis acids have been used for aldol additions, Ehels-Alder... 

Domino Processes u/ith the Aldol Reaction as Subsequent Step 291 Table 8.12 Wittig rearrangement/aldol reaction as developed by Wolfe et al. [45],... 

The allylic halide needed for the alkylation is easily made by some aldol or Wittig-style reaction to give 63 followed by reduction and conversion of OH to Br. Alkylation of phenols (p a 10) with allylic halides is very easy as a weak base such as carbonate is enough and the Claisen rearrangement merely requires heating.15... 

These amidines have been extensively applied to dehydrohalogenation in organic synthesis and in some cases DBU (1) is more effective than DBN (2) [5]. A double bond can be also introduced into organic molecules by elimination of sulfonate ester instead of the halogen atom (i.e. dehydrosulfonation in addition to dehydrohalogenation). Furthermore, these amidines can be applied to the Wittig reaction [6], aldol condensation [6], 1,3-allyl rearrangement [7] and epimerization of the (3-lactam skeleton (at Ce of the penicillic acid derivatives). Sterically hindered phenols (e.g. 2,6-di(ferf-butyl)-4-fluorophenol) are (9-acetylated with DBU (1), which is superior to sodium hydroxide in the synthesis [8]. 

Ba(OH)2 is known to cattdyze several base-catalyzed organic reactions in the solid form, Of the reactions, aldol condensation is the most common. In recent years, several organic reactions besides aldol condensation have been found to be effectively catalyzed by Ba(OH)2. These reactions are the Claisen-Schmidt reaction, esterification of acid chlorides, Williamson s ether synthesis, benzil-benzilic acid rearrangement, the synthesis of A -pyrazolines by the reaction of a,/3-unsaturated ketone with PhNHNHz Wittig-Homer reaction, and Michael addition. For these reactions, the Ba(OH)2 catalyst prepared from Ba(0H)2-8H20 by cidcination at 473 K shows the highest activity. 

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