Takeshi Imagawa

Synthesis of 2-(1-Hydroxyalkyl)acrylonitriles by the Cocatalysis of a Base and an Acid

Abstract Titled compounds are synthesized in good yields from acrylonitrile and saturated aliphatic aldehydes by the cocatalysis of tributylphophine and triethylaluminium.

Diels-Alder reaction of methyl coumalate with 1,3-dienes

Abstract Reaction of methyl coumalate ( 1b ) with 1,3-butadienes at 100° afforded the tetrahydrocoumarins ( 6 ) and the 4-methoxycarbonyltricyclo[3.2.1.0 2,7 ]octenes ( 7 ). The similar reaction of 1b with cyclohexadiene gave exclusively tetrahydronaphthalene-2-carboxylate. With cyclopentadiene, 1b afforded a product ( 10 ) resulting from the addition reaction in which cyclopentadiene acted as a dienophile. The reaction giving 6 is the first example of the reaction of a 2-pyrone as a dienophile.

Photochemical reactions of allylphenoxide anions

Abstract Photochemical behaviour of sodium allylphenoxides 1a–3a was compared with that of corresponding neutral allylphenols 1b–3b, and a striking difference was found in reactivity as well as in course of the reaction. Remarkably higher photoreactivity of allylphenoxide anions, especially that of o-allylphenoxide 1a, is ascribed to the efficiency of electron transfer. The characteristic reaction products derived only from the anions were as follows: (a) intramolecular cyclization products, indanols 9, from 2a, (b) rearranged reduction products 10 from both 2a and 3a, and (c) degradative methanol-adduct 11 from 3a. Methanol-adducts 7 and photo-reduction products 6 were formed in either case. In addition cyclization products with the participation of O atom, 4 and 5, were obtained from 1a and 1b. Occurrence of the di-π-methane rearrangement was restricted to the reaction of neutral species 1b–3b. A mechanism based on electron transfer in the excited state is suggested for the course of the photoreaction.

Diels–Alder reactions of methyl coumalate with 1,3-dienes

Diels–Alder reaction of methyl coumalate (Ib) with 1,3-dienes afforded the tetrahydrocoumarin (IV) and/or the tricyclo[3,2,1,02,7]oct-3-ene (V) in which the reaction giving (IV) is the first example of the reaction of a 2-pyrone as a dienophile.

Stereospecific synthesis of t,t-1,2,3-trisubstituted cyclopentanes and of angularly disubstituted t-hydrindanols

Abstract Anodic oxidative decarboxylation of endo-3-methoxycarbonyl-7-oxabicyclo[2.2.1]heptane-endo-2-carboxylate anion gave exclusively an oxygen-assisted Wagner-Meerwein-rearranged product, methyl 3-methoxy-2-oxabicyclo[2.2.1]heptane-anti-7-carboxylate, constituting a method for the stereospecific synthesis of c-3-acyl-t-2-methoxycarbonyl-r-1-cyclopentanols. Synthesis of 7a-methoxycarbonyl-t-hydrindane-3a,1-carbolactones was also attained.

Total synthesis of dl-hop ether, an iridoid monoterpene

Abstract An iridoid monoterpene hop ether, 2,2-dimethyl-6-methylene-3-oxabicyclo[3.3.0]octane, was first synthesized in six steps starting from the protected lactol form of 3-formyl-2-methoxy-carbonylcyclopentanol.

Cycloaddition reaction of methyl 2-pyronecarboxylates with 1,3-dienes

Abstract The experimental results of thermal cycloaddition reactions of methyl 2-pyrone-3-, 4-, 5- and 6-carboxylates with 1,3-dienes and the theoretical approach by a second order perturbation MO method are described. The sequential introduction of a methoxycarbonyl group onto a 2-pyrone ring caused a variety of selectivities in the cycloaddition reactions with 1,3-butadienes. PMO treatment based only on the frontier molecular orbitals failed to account adequately for this selectivity phenomena because the relative magnitudes of the coefficients in the HO and LU orbitals of 2-pyrones were little affected by the introduction of a substituent. PMO treatment including superjacent and subjacent orbitais along with frontier orbitais rationalized excellently the observed selectivity phenomena.

Synthesis of Methyl 2-Pyrone-4-carboxylate

Abstract As a consequence of our continuing interests in the cycloaddition reaction of the 2-pyrone derivatives,1 we have required methyl esters of four 2-pyronecarboxylic acid isomers. Whereas 2-pyrone-3-, 5-, and 6-carboxylic acids or their esters2) had been already synthesized, only 2-pyrone-4- carboxylic acid (la) is still unknown, except its 6-methyl derivative.3 In this communication we disclose the preparation of 1 by Wittig reaction between 2, 2-disubstituted acetaldehyde (2) and dimethyl 2-triphenylphosphoranediylidenesuccinate (3), followed by acid-catalyzed cyclization into the pyrone ring.

Synthesis of β, γ-Unsaturated Valerolactones

Abstract In recent years various attempts have been made to use reagent equivalents1) in order to effect reactions which are not otherwise accessible by means of conventional reagents. Particularly it is to be noted that synthetic equivalents for unreactive dienophiles, such as carbon dioxide,2,3,4) ketene,3,5) allene,6) and acetylene,7) have greatly extended the scope of the cycloaddition reactions into systems not normally generated by the thermal process.

A synthesis of γ-alkylidenebutenolides photochemical rearrangement of 2,3-epoxy-1,4-cyclohexanediones

Abstract Photo-induced rearrangement of 2,3-epoxy-1,4-cyclohexanediones was investigated for a synthesis of γ-alkylidene-γ-butyrolactones and γ-alkylidenebutenolides. Irradiation of epoxy diketones 1 and 4 in acetone gave γ-lactones, 2 and 5 , and triketones, 3 and 6 . On the other hand, in CH 2 Cl 2 , EtOAc, or PhH solution epoxy diketones 1 and 4 gave only triketones, 3 and 6 . Retro-Diels-Alder reaction of γ-lactones 5aE or 5aZ at 230° (20 mmHg) afforded γ-alkylidenebutenolides 7aE and 7aZ in addition to anthracene. According to the procedure, butenolide 7bZ , a key intermediate for the synthesis of freelingyne, was prepared. The dramatic solvent effect in the photochemical rearrangement was also discussed.