Tadaatsu Naka

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.

Lipase-catalyzed enantioselective desymmetrization of prochiral 3,3-bis(hydroxymethyl)oxindoles

Abstract Oxindoles 3b – d (91–98% ee) having a chiral quaternary carbon center at the C-3 position were prepared from readily available oxindoles 5a – c in 50–64% overall yields, in which an enantioselective desymmetrization of prochiral 1,3-diols 2b – d using a Candida rugosa lipase (Meito OF) and 1-ethoxyvinyl 2-furoate 1 was employed as the key step.

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.

Reaction of ynolate anions derived from silylketenes with electrophiles: a facile preparation of silyl ynol ethers and functionalized silylketenes

Reaction of the ynolate anions 2a,b, generated from the silylketenes 1a,b, with a variety of electrophiles 3 is investigated. The reaction with bulky and/or hard silyl chlorides, such as ButMe2SiCl, PriSiCl, (Thexyl)Me2SiCl and ButPh2SiCl, exclusively gives the silyl ynol ethers 4, while that with small or soft silyl chlorides and stannyl chlorides gives only the functionalized silylketenes 5 in modest to high yields, respectively. In the case of the reaction with small and hard Me3SiCl, initial formation of the O-trimethylsilyl ynol ether 4b and the subsequent rapid isomerization to the bis-silylketene 5a are proposed by the trapping of 4b as a cobalt complex 7b.