Dithioketals hydrolysis

Butenottdes. A synthesis of the isodehydroabietenolide (5) used a new method for preparation of a butenolide (2) which was then transformed into the benzenoid ring of 5. Thus, reaction of the ketene dithioketal 1 with dimethylsulfonium methylide followed by acid hydrolysis produced the butenolide 2 in high yield. This product was then converted via the furane 3 into the salicyclic ester 4 via a Diels-Alder reaction.1... 

The dithiane-derived anion can be generated by the action of Bu°U in THF at -78 C or with complex bases NaNH2-RONa at room temperature. Lithiated dithiane can also be prepared in situ by sonica-tion of n-butyl chloride with lithium in the presence of dithiane. Dithioacetals or ketals are resistant to acidic or basic hydrolysis. Regeneration of the carbonyl group from the dithioketal sometimes presents difficulties but can be carried out by hydrolysis in polar solvents (acetone, alcohols, acetonitrile) in the presence of metallic ions such as Hg , Cu, Ag, 71 177 qj j m ise Alternatively, alkylative hy lysis... 

Oxidative hydrolysis of an ethylene dithioketal. Cain and Welling report that the method of Corey and Erickson (4,216) for oxidative hydrolysis of... 

Oxidative hydrolysis of an ethylene dithioketal. Cain and Welling report that the method of Corey and Erickson (4,216) for oxidative hydrolysis of 2-acyl-1,3-dithianes is also useful for unmasking of ethylene dithioketals. Thus treatment of the bisethylene dithioketal (1) with 4 eq. of NBS in 10% aqueous acetone at 0° for 20 min. selectively removes the less hindered ethylene dithioketal group at C to give (2) in 80% yield. Removal of the ethylene dithioketal group at C2 with Raney nickel requires reflux in ethanol and is accompanied by reduction of the carbonyl group. 

Dithioacetals and dithioketals can be converted back to the carbonyl under acidic conditions in the presence of an excess of water because every step is reversible (just as with acetals and ketals). Aqueous hydrolysis is more difficult for dithio derivatives when compared to acetals or ketals, and water-compatible Lewis acids such as mercuric (Hg ) salts are used. Dithioacetal 68, for example, is converted back to benzaldehyde (67) when it is treated... 

The known stability of 1,3-dithians compared with open-chain dithioketals has been further exemplified by the formation and reactions of these derivatives of /3-dicarbonyl compounds. The dithians (234) were formed by reaction of the /3-keto esters with 1,3-propanedithiol in the presence of ZnCU-HCl. The products were stable to base hydrolysis unlike their open-chain counterparts, which readily break down (to 235) under these conditions. 

Real-time ultrafast 2D NMR observations of an acetal hydrolysis at natural abundance have enabled observation of the reactive hemiacetal intermediate. Mutual kinetic enantioselection (MKE) and enantioselective kinetic resolution (KR) have been explored for aldol coupling reactions of ketal- and dithioketal-protected -ketoaldehydes expected to have high Felkin diastereoface selectivity with a chiral ketone enolate. ... 

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