Magnesium catalyzed [3 + 3] heteroannulation of α-enolic dithioesters with MBH acetate: access to functionalized 3,4-dihydro-2H-thiopyrans.

Magnesium catalysis proved to be efficient towards [3 + 3] chemo- and diastereoselective heteroannulation employing racemic Morita-Baylis-Hillman (MBH) acetate as the C3 unit and α-enolic dithioester as the C2S1 unit, leading to highly substituted 3,4-dihydro-2H-thiopyrans in excellent yields. The compatibility with a wide range of functional groups makes this domino formation of C-C and C-S bonds interesting. DFT analyses for the regioselective formation of the intermediate was performed.

Visible-Light Photocatalysis of Eosin Y: HAT and Complementing MS-CPET Strategy to Trifluoromethylation of ß-Ketodithioesters with Langlois' Reagent.

A metal- and oxidant-free photoinduced strategy for thioxo sulfur-selective trifluoromethylation of ß-ketodithioesters at room temperature is reported. Excellent Z/E-stereoselectivity has been achieved with cheap and viable Langlois' reagent (CF3SO2Na, sodium triflinate) in the presence of eosin Y, which acts as a hydrogen atom transfer (HAT) catalyst. The reaction proceeds via disulfide intermediate disulfanediylbis(3-(alkylthio)-1-phenylprop-2-en-1-one) (a dimer of ß-ketodithioester) followed by complementing proton-coupled electron transfer-mediated reverse HAT cycle of eosin Y. This operationally simple and efficient protocol allows direct access to triflinated α-oxoketene dithioacetals in good to excellent yields bearing diverse synthetically useful functional groups of different electronic and steric nature.

Visible-Light-Mediated Synthesis of 1,2,4-Dithiazolidines from ß-Ketothioamides through a Hydrogen-Atom-Transfer Photocatalytic Approach of Eosin Y.

An efficient protocol for visible-light-mediated synthesis of a specific class of 1,2,4-dithiazolidines from ß-ketothioamides is devised employing eosin Y as a photoinitiator at ambient temperature in an open pot. The reaction proceeds via an in situ-generated thiyl radical followed by dimerization/deaminative cyclization cascade, enabling the creation of a dithiazolidine ring through successive formation of S-S and N-C bonds under metal- and additive-free conditions. Remarkably, the benign conditions, sustainability, and quantifying forbearance of wide horizons of functional groups are added characteristics to the strategy. The developed hydrogen-atom-transfer methodology will be helpful in postsynthetic modification via added synthetic handles.

Phosphonium ylide catalysis: a divergent diastereoselective approach to synthesize cyclic ketene acetals [thia(zolidines/zinanes)] from ß-ketothioamides and dihaloalkanes.

Phosphonium ylides are being reported here as a catalyst for the formation of thiazolidines and 1,3-thiazinanes from ß-ketothioamides (which act as a three atom N, C, and S synthon) with dihaloalkanes via [3 + 2] and [3 + 3] annulations under metal-free conditions. An N,C,S-centred chemoselective dihaloalkane-controlled cascade process has been identified for the preparation of cyclic N,S-heterocycles (thiazolidines and 1,3-thiazinanes) from identical ß-ketothioamides. The reaction proceeds via consecutive sulfur and nitrogen nucleophilic attack of the thioamide on dihaloalkanes enabling the formation of S-C and N-C bonds. The ring size of the skeletally distinct N,S-heterocycles has been efficiently tuned by switching the use of 1,2- and 1,3-dihaloalkanes as α,ß- and α,γ-dielectrophiles. It is noteworthy that the products possess Z-stereochemistry with regard to the exocyclic C[double bond, length as m-dash]C double bond at the 2-position of the ring, revealing exclusive diastereoselectivity. Since phosphorus ylides have found limited use as catalysts, control experiments revealed their behaviour as a catalyst, which not only increase the catalyst tool box, but also would contribute to the field of ylide chemistry.