Dithioesters, protonation

A mole of an organometallic first reacts with the enol proton and a second mole (not necessarily the same reagent) adds exclusively to the carbonyl function, giving (3-hydroxydithioesters in good yields. After protection of the OH group the dithioester function can be used for formation of another carbon-carbon bond, and the starting 0-oxodithioesters can be viewed as a3df or synthetic equivalents [342]. 

Metzner reports that lithium dithioenolates, which are softer nucleophiles than the corresponding carbonyl enolates, add kinetically in a 1,4-mode exclusively to ot, 3-enones and the diastereoselectivity preferences are similar to that for ester enolate additions.l43a d Typically, kinetic deprotonation of dithioesters affords predominantly the (Z)-enethiolate (170) which is opposite to that for esters 139 thus, with ( )-enones, anti adducts (172) are obtained. In contrast, the addition of methyl dithioacetate to ot,P-disubstituted enones affords predominantly syn adducts (174 and 175) which is a consequence of intramolecular protonation of the resultant enolate (Scheme 68).143e... 

Sulfur as Heteroatom. Thiols and sulfides are protonated on sulfur in superacid media and give mono- and dialkylsulfonium ions, respectively.136 Thio-carboxylic acids, 5-alkyl esters, thioesters, dithioesters, and thiocarbonates in similar media also form stable protonated ions541,647 such as cations 348-353. 

A general way to achieve thiophilic addition is to use sulfines [149]. The sulfur atom of thiocarbonyl oxides is selectively attacked by carbanions. We have applied this property to aliphatic dithioester oxides and shown [150] that, despite the probably high acidity of the a-protons, thiophilic addition of alkyllithiums is observed, leading to stabilised carbanions. After treatment with electrophiles, dithioacetal oxides were obtained. From a synthetic point of view, it is worthy of note that these adducts are much more easily... 

Chloranil oxidized a variety of methylarsenic(iii) esters, amides, or cyclic thioesters, products such as (89), for example, being obtained from a dithioester of methylarsonous acid. ° The analogous reaction with 2-iodo-l,3,2-dihetero-arsolans, however, proceeded with simultaneous cleavage of the As—I bond and formation of the spirocyclic arsenic(v) compound (90). The six-co-ordinate arsenic(v) anions (91) were produced by addition of an alcohol or phenol to an arsolan in the presence of triethylamine, the latter abstracting a proton and forming the required cation. ... 

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