Yasushi Takebe

Lipase-Catalyzed Domino Kinetic Resolution/Intramolecular Diels–Alder Reaction: One-Pot Synthesis of Optically Active 7-Oxabicyclo[2.2.1]heptenes from Furfuryl Alcohols and β-Substituted Acrylic Acids

The first lipase-catalyzed domino reaction is described in which the acyl moiety formed during the enzymatic kinetic resolution of furfuryl alcohols (+/-)-3 with a 1-ethoxyvinyl ester 2 was utilized as a part of the constituent structure for the subsequent Diels-Alder reaction. The preparation of ester 2 from carboxylic acid 1 and the subsequent domino reaction were carried out in a one-pot reaction. Therefore, this procedure provides a convenient preparation of the optically active 7-oxabicyclo[2.2.1]heptene derivatives 5, which has five chiral, non-racemic carbon centers, from achiral 1 and racemic 3. The overall efficiency of this process was dependent on the substituent at the C-3 position of 3, and the use of the 3-methylfurfuryl derivatives, (+/-)-3 b and (+/-)-3 f, exclusively produced diastereoselectivity with excellent enantioselectivity to give (2R)-syn-5 (91->/=99 % ee) and (S)-3 (96->/=99 % ee). Similar procedures starting from the 3-bromofurfuryl alcohols (+/-)-3 h-j provided the cycloadducts (2R)-syn-5 j-q (93->/=99 % ee), in which the bromo group was utilized for the installation of bulky substituents to the 7-oxabicycloheptene core.

1-Ethoxyvinyl acetate as a novel, highly reactive, and reliable acyl donor for enzymatic resolution of alcohols

Abstract 1-Ethoxyvinyl acetate 3 was found to be a high performance acyl donor for enzymatic resolution of alcohols featuring that (i) 3 shows high reactivity and high selectivity comparable to the most widely used vinyl acetate 1 and (ii) reaction of 3 generates low reactivity ethyl acetate 6 as a single side product, while that of 1 releases unfavorable acetaldehyde 4 .

Enzyme-catalyzed asymmetrization of 2,2-disubstituted 1,3-propanediols using 1-ethoxyvinyl esters

Abstract The lipase-catalyzed asymmetrization of the prochiral 2,2-disubstituted 1,3-propanediols 1, 6, and 9 was studied using various types of 1-ethoxyvinyl esters 2. Among them, the use of the benzoate 2f provided good chemical and optical yields of the products 3, 7, and 10 bearing chiral quaternary carbon centers which are fairly stable against racemization.

An unprecedented cleavage of the β-lactam ring: a novel synthesis of acyclic N,O- and N,S-acetals

A new synthesis of acyclic N,O-acetals 3 and N,S-acetals 5 has been devised by way of a trimethylsilyl trifluoromethanesulfonate promoted formal 2,3-bond fragmentation of 4-heteroatom substituted azetidinones 1 and 4, respectively. This reaction proceeds by nucleophilic attack of a nitrile group of the solvent on the cation intermediate A. However, when there is a second nucleophile such as azidotrimethylsilane in the reaction system, no solvent attack occurs but, rather, the second nucleophile attacks the intermediate to form novel α-azido sulfides 6.

Conversions of thiochroman-4-ones into 1,2-benzothiazepine, benzo-[b]thiophen, and 1,2-benzisothiazole systems via sulphimide intermediates

Reaction of thiochroman-4-ones (1a–g) with chloramine-T gave the corresponding N-tosylsulphimides (2a–g) and sulphoxides (5a–g). The N-tosylsulphimides (2a–d), on reaction with triethylamine in chloroform, gave 2-tosyl-2,3-dihydro-1,2-benzothiazepin-5(4H)-ones (3a–d), but the 2-methyl congeners (2e and f) yielded 2-crotonoyl-N-tosylbenzenesulphenamides (4e and f). When the reaction was carried out in acetonitrile, (2e and f) afforded (3e and f) and (Z)-2-ethylidene-2,3-dihydrobenzo [b]thiophen-3(2H)-ones (7e and f). The 2,2-dimethyl derivative (2g) led to only (4g) and (7g). Heating (2a–c) in acetic acid gave Diels–Alder dimers (6a–c) of 2-methylidene-2,3-dihydrobenzo [b]thiophen-3-ones, and (2e–g), upon heating in chloroform containing acetic acid, gave (7e–g). S-Amination of (1a, b, and d–f) with O-mesitylenesulphonylhydroxylamine followed by alkaline treatment gave 3-vinyl-1,2-benzisothiazoles (11a, b, and d–f).

1-Ethoxyvinyl 2-furoate, an efficient acyl donor for the lipase-catalyzed enantioselective desymmetrization of prochiral 2,2-disubstituted propane-1,3-diols and meso-1,2-diols

A novel acyl donor, 1-ethoxyvinyl 2-furoate, was found to produce the title reactions with high enantiotopic selectivity, high reactivity and stability of the products under various conditions.

Rearrangement of 4-oxothiochroman-1-io(bismethoxycarbonyl)methanides to tetrahydro-1-benzothiepin-5-ones

Heating thiochroman-4-ones with dimethyl diazomalonate without solvent or in refluxing toluene in the presence of copper(II) sulphate gave the corresponding bismethoxycarbonylmethanides (4) and dimethyl 5-oxo-2,3,4,5-tetrahydro-1-benzothiepin-2,2-dicarboxylates (5). Treatment of the sulphonium methanides (4) with triethylamine afforded (5).