Thionation of lactones

Cyclic ethers from lactones. The ready addition of RLi to the C=S group of thionolactones (14, 9) has been used to prepare functionalized cyclic ethers from lactones of the same ring size. The first step involves Lawesson thionation of lactone... 

Monothioacetals 1,3-Oxathiolanes Thiolactams S extrusion, 59-60, 261 Thiols synthesis from haloalkanes, 169, 269 Thionation of lactones, 110-111 Thiones olefination of, 35 Thionocarbonates. See Carbonothioates Thionolactones, 110-111 Thionyl chloride prepn. of acyl halides, 143 prepn. of carboxylic esters, 347 prepn. of haloalkanes from alcohols, 32 Thiophenoi. See Benzenethiol Thiotosylatc. See Benzenesulfonothioic add... 

N-AUcylthiolactams.2 N-Alkyllactamscan be converted into N-alkylthiolactams by the same method previously used to convert lactones into thiolactones (10, 417). However, the method is not applicable to thionation of acyclic N,N-disubstituted amides [RC(S)OR is obtained instead]. 

Thiono Esters and Lactones. Although thiono esters can be conveniently prepared via imidates, the introduction of LR for the thionation of esters represents a great advance in synthetic methodology since ordinary esters are used as educts and P4S10 only reacts with esters if enforced reaction conditions are applied, under which many thiono esters decompose. Facile conversion of... 

Thionation of Carboxylate Esters and Lactones. The reaction of esters and lactones with LR represents a well-established method for the synthesis of the corresponding thiocarbony 1 deriva-tives. - In fact, LR is the much superior reagent for the thionation of esters as compared with phosphorus pentasullide. Open-chain thionoesters have been conveniently obtained. Interestingly, natural triglycerides also smoothly react with LR to yield pure tristhionotriglycerides. Even better results are obtained with carboxylate esters if the improved solubilized LR or microwave irradiation are applied. The method has particularly been used for the preparation of cyclic thionoesters. Obviously there are very few structural or other restrictions that inhibit the formation of y-,S-, or macrocyclic thionolactones. Once more, microwave irradiation significantly improves the re-... 

Thionation of Carbonyl Compounds. Diaryl thioketones and 2,4-bis(diphenylmethylene)cyclobutane-l,3-dithione were obtained on reaction of the corresponding ketones with DR. On the other hand, JR was utilized to thionate selectively the carbonyl group of benzil monophenylimine. If carboxylic esters or lactones are reacted with DR, dithiocarboxylic esters or dithiolac-tones are formed, i.e. the carbonyl group is thionated and the alkoxy group is substituted by an aUcylthio group. Bis(5-methyl-2-thienyl) disulfide is produced in this way from a butenolide (eqS). ... 

The thionation of five-, six-, and seven-membered ring lactones by the combination of LR and HMDO under microwave irradiation has been reported. The reactions were very fast, being completed in a matter of minutes. In initial trials using )/-dodecalactone as substrate (eq 13) and microwave radiation, thionation by LR alone, by CR, and by the combination of LR/HMDO was compared. 

After completion of the pilot studies with y-dodecalactone, thionation of a series of y-lactones was examined and found in most cases to give the corresponding thionolactone with good yield and selectivity. Yields obtained with the one 3-lactone and the one e-lactone examined were less satisfactory (44% and 15%, respectively). 

The reaction is completed within 5-15 min if tetralin at 210°C is used as sol vent. Also, dithio-7-lactones, including dithiophthalides and dithio-a-pyrones, are formed smoothly whereas the hitherto unknown simple p- or 8-dithiolactones cannot be prepared, neither with LR nor by any other method. Interestingly, dithiopilocarpine is formed as a mixture of diastereomers on reaction of pilocarpine with LR (eq 16), i.e. both oxygen atoms of (12) are replaced by sulfur. In an interesting sequence of thionation and rearrangement reactions, three different thiono analogs of 1,8-naphthalic anhydride were prepared (eq 17). ... 

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