Sulfoxides Knoevenagel reaction

Sulfinyl dienes and vinyl sulfoxides have rarely been used in asymmetric hete-ro-Diels-Alder reactions [145]. The first example was reported in 1992 and describes an intramolecular cycloaddition using a heterodiene bearing a chiral sulfinyl group [146a]. In this paper, the conversion of a-p-tolylsulfinyl a,ft-unsaturated ketone 176 (prepared by Knoevenagel reaction of 3-methylcitronellal and (S)-p-toluenesulfinylacetone) into the hetero-Diels-Alder adducts 177... 

Another study in double stereodifferentiation of the Knoevenagel reaction (chiral sulfoxides with chiral aldehydes) showed the induction to be dependent on the absolute configuration of and substituents on the sulfoxide, as well as on the amount of base used88. 

Allyl sulfoxide systems appropriate for a transformation to allylic alcohols can also be generated by other preparative methods, e.g. by isomerization of aryl vinyl sulfoxides. Such an isomerization occurs in connection with a Knoevenagel reaction of (10) with aldehydes leading finally to y-hydroxy-a,3-unsatu-rated systems (11), which can easily be transformed into a,3-unsaturated y-lactones (12 Scheme 17). ... 

Di-tert-butyl methylenemalonate was originally prepared by phenyl-sulfenylation of di-tert-butyl methylmalonate and thermal elimination of the related sulfoxide.8 Because methylenemalonate esters are customarily prepared by Knoevenagel-type condensation of malonic esters with formaldehyde equivalents, the considerably more convenient procedure described herein was subsequently adapted from Bachman and Tanner s study using paraformaldehyde under metal ion catalysis.39 The approximately 6% di-tert-butyl malonate accompanying the product has presented no interference in the aforementioned reactions with nucleophilic alkenes under neutral or acidic conditions, but its presence should be taken into consideration in other applications. 

Lasperas et al. [73,74,78] have studied the Knoevenagel condensation between benzaldehyde (1) and ethyl cyanoacetate (2) in the presence of over-exchanged CsY zeolites. The reaction was performed under a nitrogen atmosphere in dimethyl sulfoxide (DMSO), the best solvent for eliminating interference from the non-catalyzed reaction. The use of equimolar amounts of each reactant suppressed successive Michael addition between ethyl cyanoacetate and ethyl cyanocinna-mate (3) to give compound 4 (Scheme 5) this resulted in high selectivity for the Knoevenagel product (3) (95 % at 90 % conversion). 

This reaction was used in a procedure for homologation of aromatic aldehydes, as illustrated for conversion of benzaldehyde into phenylacetaldehyde (5). The first step is a Knoevenagel-like reaction with methyl methylthiomethyl sulfoxide... 

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