Morita-Baylis-Hillman adducts

Some additional examples, where the stereochemical outcome of the cycloaddition to chiral alkenes has been explained in terms of the Honk—Jager model, should also be mentioned. The diastereomer ratio found in the reaction of y-oxy-a,p-unsamrated sulfones (166), with Morita-Baylis-Hillman adducts [i.e., ot-(a -hydro-xyalkyl)-acrylates (167)] (Scheme 6.27), with dispiroketal-protected 3-butene-l,2-diol (168), and with a,p-unsamrated carbonyl sugar and sugar nitroolefin (169) derivatives, all agree well with this model. 

Ab initio calculations also confirm that the use of an allyl magnesium alkoxide in place of the alcohol functionality will lead to high or complete stereoselectivity (138). When homoallylic alcohols are used, the Kanemasa protocol afforded the respective isoxazolines with poor stereoselectivity ( 55 45) in the case of terminal aUcenes, but with very high diastereoselectivity (up to 96 4) in the reaction of cis-1,2-disubstituted olefins (136). Extension of this concept to the reaction of a-silyl allyl alcohols also proved feasible and produced the syn (threo) adducts as nearly pure diastereomers (>94 6) (137). Thus, the normal stereoselectivity of the cycloaddition to the Morita-Baylis-Hillman adducts (anti > syn, see above) can be reversed by prior addition of a Grignard reagent (176,177). Both this reversal... 

Intramolecular hydrogen bonding has been proposed to facilitate nucleophilic addition of sulfones to the Morita-Baylis-Hillman adducts in a single step to produce the substituted allyl sulfones.178... 

A new route to 6-substituted pyrrolo[2,l-b]thiazoles 58 takes advantage of an intramolecular thermal cyclization of acetates 56 <07S3037>. These acetates are easily derived from the Morita-Baylis-Hillman adducts of thiazole-2-carboxaldehyde. This strategy has also been extended to the synthesis of the tricyclic analogs 60. 

AT-Tosylaldimmes 293 reacted with excess allene 294 in the presence of tertiary phosphine promoters to give a mixture of 295 (major) and 296 (minor). The normal Morita-Baylis-Hillman adducts 297, which were formed on catalysis by DMAP, were not intermediates in the formation of the piperidines. A mechanistic rationale for the different reactions was presented (Scheme 89) 050BC3686>. 

The practical value of DMP as a reagent has been extended to various other synthetically useful oxidative transformations, such as the dehydration of primary alcohols under extraordinarily mild conditions [1276], synthesis of various polycyclic heterocycles via the oxidative cascade cyclization of anilides with pendant double bonds [1277], one-pot oxidative allylation of Morita-Baylis-Hillman adducts with allyltrimethylsilane promoted by DMP/Bp3-OEt2 [1278], synthesis of 2-amino-l,4-benzoquinone-4-phenylimides from anilines via DMP oxidation [1279], a-tosyloxylation of ketones using DMP and p-toluenesulfonic acid [1280] and the DMP-mediated oxidative aromatization of 1,3,5-trisubstitutedpyrazolines [1281]. 

Subsequently, multicomponent reactions were less explored. In 1998, Richter and Jung reported a three-component reaction of a polymer-bound acrylate, aldehydes and sulfonamides in the presence of DABCO as catalyst in dioxane. After cleavage from the polymer support, the desired Morita-Baylis-Hillman adducts 214 were obtained in good yields with moderate to high purities (Scheme 1.81). 

Transformations of Functional Groups in Morita-Baylis-Hillman Adducts... 

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