Malonates sulfenylation

Tlie bifunctional sulfenyl chloride 213 was obtained by chlorination of 144 in good yield, although excessive chlorination led to the saturated compound 214 (94CB533). A series of compounds 215-220 were obtained from 213 by reactions with secondary amines ferf-butyl methyl ketone hexane-2,4-dione 2,6-dimethylcyclohexanone diethyl malonate and acetylacetone, respectively. 

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. 

The sulfenylation of metalloimines is equally applicable to ketones, although using more reactive sulfur electrophiles it is possible to bring about reaction on the unmetallated enamine. ° Sulfenylation of ketone enol silyl ethers also proceeds well with the more reactive sulfur species. Sulfenamides and their derivatives e.g. 11) are particularly suited to the direct sulfenylation of ketones and active methylene compounds such as -diketones, -keto esters and malonates, which undergo facile reaction at room temperature (equation 5). This procedure, however, does not appear to have been exploited for the dehydrogenation of active methylene compounds icf. Section 2.2.4.1). By preparing the dianion (13)... 

The a-sulfenyl group can be replaced by a benzothiazolthio group, as demonstrated in the synthesis of the 1,4-diketone (CXXXIV), a precursor of cw-jasmone [Eq. (65)] [10]. The geminal dicarboxylic acid (CXXXVI) can also be transformed into the 1,4-diketone (CXXXIV) by electrochemical decarboxylation as in Eq. (66) [6], suggesting that the substituted malonic acid group is synthetically equivalent to a carbonyl group. 

A stable aliphatic thioacyl chloride (44) was obtained according to equation (42) and used in alcoholysis reactions to prepare thioxo malonates (45)."° A mixture of sulfenyl chloride (46) and trisulfide (47), which does not however contain an a-oxothioacyl chloride, also yields thioxoesters on base-catalyzed reaction with methanol (equation 43). ... 

The same authors also reported that treatment of the a-chloro sulfenyl chlorides 215 (obtained from the pyridine-catalyzed reaction between dialkyl malonates and thionyl chloride) with sodium trithiocarbonate gave 1,2,4,5-tetrathianes 211 in good yield (Equation 19) <2002EJ02039>. 

Tetrathianes. (1) Oxidative dimerization of a,a-disuhstituted alkanedithioic acid dianions (Scheme 38) or 1,1-dithiols (Equation 17) - very limited examples and a-monosuhstituted alkanedithioic acids decompose (2) reductive or pyrolytic dimerization of gi OT-disulfenyl dichlorides (Equation 18) - only malonate-derived examples (3) reaction of a-chloro sulfenyl chlorides with sodium trithiocarhonate (Equation 19) - only malonate-derived examples (4) sodium thiophenoxide-catalyzed reaction of thioketones with elemental sulfur (5) reaction of benzo-furan-3(2//)-one with S2CI2" (6) UV irradiation of a CS2 solution of a diazirine (7) reaction of a 2,2,4-trisubstituted-1,3-dithietane with Oxone (Scheme 54)". Method (4) is the most convenient and general of these. 

ProIine-derived phosphines bearing various sulfenyl substituents have been developed Use of 21a-g as chiral ligands provided (5)-2, except 21e [(/ )-2], with 31-88% ee in the Pd-catalyzed allylic alkylation of 1 with dimethyl malonate using [Pd(7r-allylX l]2, BSA, and AcONa in dichloromethane at room temperature. Increasing the steric bulk of the substituents of the sulfenyl groups results in enhanced enantiocontrol (21g. provides 88% ee). The thiophene ligand 22 provides (R)-2 with 30% ee (Scheme 12). 

Chlorination of Activated Methylene Groups. Triflyl chloride was used for the high yielding chlorination of carbon acids, and this reaction was applied to the synthesis of simple 2,2-disubstituted heterocycles. This method has been extended to the preparation of heterocycles fused with -lactams. Treatment of a hydroxyphenylazetidinone with triflyl chloride and triethy-lamine afforded a hemiaminal in 90% yield, through the chlorination of the dibenzyl malonate moiety (eq 11). Performing the same transformation on a mercapto- -lactam precursor led to the formation of a sulfenyl chloride intermediate rather than to chlorination of the malonate moiety. ... 

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