Propargylic dithioacetals

Propargylic dithioacetals have been shown to be good starting materials for the synthesis of trisubstituted furans. Recently, a modification appeared, which demonstrated that these compounds could also be used to prepare tetrasubstituted furans in good yields <06SL1209>. 

Reaction of propargylic dithioacetals 74 with organocopper reagent followed by treatment with an aldehyde and then with acid provides 2,3,5-trisubstituted furans in moderate to good yields <00JA4992>. 

Propargyl dithioacetals undergo a Au-catalysed rearrangement to indeno[6]dithiins 68 <07JOC1192>. 

Various propargylic dithioacetals react with organomagnesium compounds to yield substituted allenes. Alkynyl oxiranes like 137 lead to 2,3-allenols of type 138 under iron catalysis with good chirality transfer (Scheme 2-50). ... 

As known from the Umpolung reactions, dithioacetals can be deprotonated efficiently among others [230, 306], a recent application is 122 [307] (Scheme 1.54). Even basic aluminum oxide can catalyze these isomerizations. One older example reports the isomerization of an S-propargyl phosphanesulfide to the allene [308],... 

The thiophilic addition of Grignard reagents was also carried out with S-allylic and propargylic dithioates. In these cases a [2, 3] sigmatropic rearrangement of the magnesiocarbanion occurred, and alkylation at sulfur yielded the dithioacetals of (i-unsaturated ketones [334] or of allenic ketones [335]. 

The reaction of propargylic esters with aldehydes and hydrogen sulfide in the presence of boron trifluoride etherate leads to 1,3-dithiins (86) (Equation (56)) <71T5753>. Dieckmann cyclization of suitably substituted acyclic 1,3-dithioacetals gives rise to l,3-dithian-5-ones (87) (Equation (57)) <59LA(624)79, 63LA(661)84>. 

The acyl migration of benzylic acetates was also applied for the synthesis of indenes (equation 87). Isomeric indenes were also obtained as minor products. The transformation was actually shown to proceed via allenes, which could be independently prepared by Ag(I)-catalyzed 1,3-acetate migration from the same starting materials. Propargylic sulfides and dithioacetals undergo similar transformations as propargylic carboxylates to give indene derivatives with Au(I) or Au(III) catalysts. 

A convenient base-mediated strategy to synthesize 3-aroyl-4-methyl-(or benzyl)-2-methylthio furans (tri-substituted furans) was developed through domino coupling/annulation between readily available a-oxo ketene dithioacetals and propargyl alcohols (140BC8947). 

Indenes can be synthesized via intramolecular hydroarylation of propargyl acetates catalyzed by NHC gold(I) complexes [127, 128]. The formation of the indenes proceeds via a 1,3-shift to form an allene, followed by the hydroarylation (Scheme 1.8). Notably, this reaction requires strictly anhydrous conditions, because conjugated enones and enals are isolated in the presence of water [129]. Related transformations include reaction with propagyl sulphides or dithioacetals. 

SCHEME 14 Formation of pyrroles via deacetylative [3+2] cydoaddition of a-acyl ketene dithioacetals and commercially available propargyl... 

C.-Q. Ren, C.-H. Di, Y.-L. Zhao, J.-P. Zhang, [3 + 2] cycloadditions of a-acyl ketene dithioacetals with propargyl amines pyrrole synthesis in water. Tetrahedron Lett. 54 (2013) 1478-1481. 

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