Free-radical hydrothiolation of the endocyclic double bond of enoses is reported. Reaction between 2-acetoxy-D-glucal and a range of thiols including amino acid, peptide, glycosyl thiols, and sugars with primary or secondary thiol functions gave S-linked α-glucoconjugates and S-disaccharides with full regio- and stereoselectivity. Addition of glycosyl thiols to a 2,3-unsaturated glycoside also proceeded with good selectivity and afforded a series of 3-deoxy-S-disaccharides.
Some important results from the past seven years on the ringchain tautomerism of 1,3-heterocycles are reviewed, including substituent effects on the tautomeric equilibria and synthetic applications of this phenomenon. The structures and reactivities of numerous five-and six-membered, saturated, N-unsubstituted 1,3-X,N-heterocycles (X = O, S, NR) can be characterized by the ring-chain tautomeric equilibria of the 1,3-X,N-heterocycles and the corresponding Schiff bases;
By means of simple or domino ring-closure reactions of 1-(α-aminobenzyl)-2-naphthol (Betti base: 1), 1-aminomethyl-2-naphthol (2) and 2-(α-aminobenzyl)-1-naphthol (reverse Betti base: 3) with phosgene, ethyl benzimidate, 2-carboxybenzaldehyde, levulinic acid, salicylaldehyde/formalin or salicylaldehyde/acetaldehyde, naphth[1,2-e][1,3]oxazine and naphth[2,1-e][1,3]oxazine derivatives were prepared. All of the nitrogen-bridged polycyclic derivatives of 1 and 3 containing a number of centers of asymmetry were formed with nearly complete diastereoselectivity. Considerable differences were observed in the ringclosing abilities of the unsubstituted and phenyl-substituted aminonaphthols 1 and 2 and of the regioisomeric compounds 1 and 3.
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