Search

A method for the synthesis of octalactin B is established via a new and quite effective mixed-anhydride lactonization for the synthesis of an eight-membered ring moiety using 2-methyl-6-nitrobenzoic anhydride with DMAP. Both an optically active linear precursor of the lactone and a side chain of octalactins are prepared by the enantioselective aldol reaction of ketene silyl acetals with aldehydes.

A new method for the synthesis of optically active anti-vic-hydroxymethyl units that correspond to anti-aldol derivatives is developed by way of successive enantioselective aldol and diastereoselective desulfurization reactions.

An effective method for the preparation of 8-membered ring enone, (4S,5R,7R,8R)-4,8-bis(benzyloxy)-7-(t-butyldimethylsiloxy)-5-(4-methoxybenzyloxy)-2,6,6-trimethylcyclooct-2-enone (1), in sufficien...

A new method for the synthesis of optically active anti-vic-hydroxymethyl units that correspond to anti-aldol derivatives is developed by way of successive enantioselective aldol and diastereoselective desulfurization reactions.

Various carboxylic esters were obtained in excellent yields with high chemoselectivities from nearly equimolar amounts of carboxylic acids and alcohols using 2-methyl-6-nitrobenzoic anhydride with triethylamine in the presence of a catalytic amount of 4-(dimethylamino)pyridine.

An efficient method for the synthesis of (+)-buergerinin F is established via the enantioselective aldol reaction of a tetra-substituted ketene silyl acetal with crotonaldehyde, followed by intramolecular Wacker-type ketalization.

Octalactin A, an antitumor agent containing an eight-membered lactone moiety, has been stereoselectively prepared by means of enantioselective aldol reactions of selected silyl enolates with achiral aldehydes, promoted by a chiral Sn(II) complex. The medium-sized lactone part was effectively constructed by way of a new and rapid mixed-anhydride lactonization using 2-methyl-6-nitrobenzoic anhydride (MNBA) with a catalytic amount of 4-(dimethylamino)pyridine (DMAP) or 4-(dimethylamino)pyridine 1-oxide (DMAPO). The use of only 5 mol % of DMAP or 2 mol % of DMAPO rapidly promoted formation of the medium-sized ring of the octalactin, demonstrating the remarkable efficiency of the new lactonization protocol.

A variety of lactones were prepared in high yields at room temperature from the corresponding ω-hydroxycarboxylic acids using 2-methyl-6-nitrobenzoic anhydride in the presence of 4-(dimethylamino)pyridine. A similar reaction also occurs with triethylamine when using a catalytic amount of 4-(dimethylamino)pyridine 1-oxide as an effective promoter for the intramolecular condensation reaction. These methods were successfully applied to the synthesis of erythro-aleuritic acid lactone and the efficiency of the cyclizations is compared to those of other reported mixed anhydride methods.

An effective method for the preparation of 8-membered ring enone, (4S,5R,7R,8R)-4,8-bis(benzyloxy)-7-(t-butyldimethylsiloxy)-5-(4-methoxybenzyloxy)-2,6,6-trimethylcyclooct-2-enone (1), in sufficien...

Various carboxylic esters were obtained in excellent yields with high chemoselectivities from nearly equimolar amounts of carboxylic acids and alcohols using 2-methyl-6-nitrobenzoic anhydride with triethylamine in the presence of a catalytic amount of 4-(dimethylamino)pyridine.

An effective method for the preparation of 8-membered ring enone 1 in sufficient quantities was developed. First, optically active trialkoxyaldehyde 3 was prepared by diastereoselective dihydroxylation of olefin 7 derived from D-pantolactone. Secondly, 8-chloro-7-oxoaldehydes 20α,β were newly synthesized by the following reactions: namely, MgBr2·OEt2-mediated diastereoselective aldol reaction of the aldehyde 3 with ketene (trimethylsilyl) acetal 15, direct 1,1-dichloroethylation of ester 17 with 1,1-dichloroethyllithium, and partial dehalogenation of the resulting α,α-dichloroethyl ketone 18 with nBu3SnH. Lastly, the chiral 8-chloro-7-oxoaldehydes 20α,β were converted to the 8-membered ring enone 1 by SmI2-mediated aldol cyclization.