. J. Chem. 56,226 (1978).Vinylphosphonates 11, readily prepared from diethyl carbomethoxymethyl phosphonate (10) react with a-mercaptocarbonyl compounds to afford substituted 3-carbomethoxy-2,5-dihydrothiophenes in excellent yields. The scope of this synthesis is indicated and the use of the products in the synthesis of substituted 2-carboxy-1,3-butadienes is illustrated. JOHN M. MCINTOSH et ROBERT A. SIELER. Can. J. Chem. 56,226 (1978).Les vinylphosphonates 11 qui peuvent Ctre prtparks facilement a partir du phosphonate de carbomCthoxyn~Cthyle et de dikthyle (lo), reagissent avec des composes a-mercaptocarbonyle pour conduire aux carbomethoxy-3 dihydro-2,s thiophenes substituis et ceci avec d'excellents rendements. On indique la genkralitt de cette synthtse et on illustre aussi l'utilisation des produits dans la synthese de carboxy-2 butadienes-1,3 substitues.[Traduit par le journal]In recent years, we have been engaged in delineating the reactions of mercaptocarbonyl compounds with various types of Michael acceptors. Much of that work has centered on the use of vinylphosphonium salts (1) and we have shown that substituted 2,5-dihydrothiophenes (1) and dihydrothiopyrans (2) are readily prepared using these reagents. These products are useful synthons for a variety of organic structures, in particular, as sources of specifically alkylated conjugated dienes (3). While the synthesis is highly successful for alkylated materials, compounds having functional groups directly attached to the ring offer more obstacles. For instance, methoxy-or carboalkoxy-substituted dienes would require the preparation of dihydrothiophenes of general structure 2. These in turn would necessitate the use of either 3 as the vinyl salt or 4 as the niercaptocarbonyl compound. Esters (40) do not gen-erally give olefins on treatment with a phosphorane (4) although some exceptions are known (5), and cr-keto-P-mercaptoesters (4b) are both difficult to prepare and offer ambiguity in the site of attack by a phosphorane. A single example of 30 is k~lown (6) and it does not behave satisfactorily in the annulation reaction (Ic). Finally, compounds of type 3b are not readily available and the phosphorane formed by attack of thiolate ion would be of a type (5a) well known to react with aldehydes but very poorly with ketones (7).It is known that phosphonate anions (5b) are more nucleophilic than 5a (4) and thus the use of vinylphosphonates (6) was suggested. Furthermore, a considerable number of compounds of type 6 bearing a variety of functionality are known (see for example ref. 8) and they have been shown to undergo addition reactions with nucleophiles (9). However, there is 50 x = P~, P 60 X = OR 5h X = P(O)(OR), 6b X = COOR ample evidence in the literature (10) to indicate that a Wittig-type reaction of phosphonate anions only proceeds well when electron-withdrawing substituents are adjacent to phosphorus. Thus, we centered our attention on the preparation and use of compounds of type 6b. The importance of these functionalized dihydrothiophenes li...
Die durch Kondensationen von Methoxycarbonylmethanphosphonsäurediethylester mit geeigneten Aldehyden dargestellten ungesättigten Phosphonate (I) (Ausb. 55‐87%) werden mit Mercaptocarbonylverbindungen (II) in Gegenwart von NEt3 oder NaH zu den Titelverbindungen (III) (IR‐Banden, 1H‐NMR‐Spektren) umgesetzt.
Mercapto‐acetalaldehyd (I) reagiert mit den Vinylphosphonsäureestern (II) zu den Dihydrothiophe‐ nen (III), die zu den Sulfonen (V) oxidiert werden können.
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