Selected 5‐substituted derivatives 4 of 1,1‐diethoxy‐5‐hydroxypent‐3‐yn‐2‐one were treated with propane‐1,3‐dithiol under various conditions. The unprotected hydroxy ketones underwent cyclization during the dithiol addition and gave the corresponding 3‐(diethoxymethyl)‐2‐oxa‐6,10‐dithiaspiro[4.5]decan‐3‐ols 5 in 80–90% yield as the only products (Scheme 3 and Table 1). These products can be regarded as partly modified carbohydrates in the furanose form. When the benzyl‐protected analogues 10‐Bn of the 1,1‐diethoxy‐5‐hydroxypent‐3‐yn‐2‐one derivatives were treated with the same dithiol, however, no cyclization occurred; instead the corresponding 3‐{2‐[(benzyloxy)methyl]‐1,3‐dithian‐2‐yl}‐1,1‐diethoxypropan‐2‐one derivatives 11‐Bn were formed in good yield (up to 99%; Table 4). These 1,3‐dithianes were and are in the process of being converted to a number of new carbohydrate analogues, and here are reported high‐yield syntheses of functionalized molecules 17 belonging to the 5,5‐diethoxy‐1,4‐dihydroxypentan‐2‐one family of compounds (Table 7), via 15‐Bn (Table 5) and 16‐Bn (Table 6 and Scheme 8).
Propane-1,3-dithiol to α,β-Unsaturated Ketones. -MeONa-mediated addition of dithiol (II) to alkynes (I) is accompanied by an intramolecular cyclization to afford spiro compounds (III), which can be regarded as partly modified furanose derivatives. Standard transformations of the corresponding non-cyclized dithians (VII) afford compounds (VIII), which are versatile precursors to a number of modified carbohydrates, such as (IX) and (XI). -(VALDERSNES, S.; APELAND, I.; FLEMMEN, G.; SYDNES*, L. K.; Helv. Chim. Acta 95 (2012) 11, 2099-2122, http://dx.
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