Masashi Hamaguchi

Reaction of vinylcarbenoids with benzaldehydes: formation of vinylcarbonyl ylides followed by ring closure to oxiranes and dihydrofurans.

Rh2(OAc)4-catalyzed reaction of vinyldiazo compound 1a in the presence of p-methoxybenz- 2a, mesit- 2b, and p-chlorobenzaldehyde 2c gave a mixture of isomeric vinyloxiranes 3a−c and 4a−c, and sterically unstable (E)-dihydrofurans 5a−c, but not stable (Z)-dihydrofurans 6. However, the reactions with p-nitro- 2d and 2,4-dinitrobenzaldehyde 2e gave (Z)-dihydrofurans 6d,e along with 3d, 4d, and 5d,e. The reaction in the presence of maleic anhydride and dimethyl fumarate gave single 1,3-dipolar cycloadducts 11 and 13, respectively, indicating that a single conformer, the sterically unstable endo-aryl-endo-cyanostyryl carbonyl ylide 14 (15), is initially formed in the reaction of 1 with 2. It was concluded that the endo-vinyl-exo-aryl vinylcarbonyl ylides 17a−c arising from 2a−c undergo disrotatory cylization to exlusively produce 5, whereas the ylides 17d,e arising from 2d,e undergo partly symmetry-forbidden conrotaory cyclization to sterically stable trans-diaryldihydrofurans 6d,e as well as the symmetry-allo...

Reaction of vinylcarbenoids with aldehydes: formation of vinylcarbonyl ylides followed by ring closure to oxiranes and dihydrofurans

Rh(2)(OAc)(4)-catalyzed reaction of vinyldiazo compound 1a in the presence of p-methoxybenz- 2a, mesit- 2b, and p-chlorobenzaldehyde 2c gave a mixture of isomeric vinyloxiranes 3a-c and 4a-c, and sterically unstable (E)-dihydrofurans 5a-c, but not stable (Z)-dihydrofurans 6. However, the reactions with p-nitro- 2d and 2,4-dinitrobenzaldehyde 2e gave (Z)-dihydrofurans 6d,e along with 3d, 4d, and 5d,e. The reaction in the presence of maleic anhydride and dimethyl fumarate gave single 1,3-dipolar cycloadducts 11 and 13, respectively, indicating that a single conformer, the sterically unstable endo-aryl-endo-cyanostyryl carbonyl ylide 14 (15), is initially formed in the reaction of 1 with 2. It was concluded that the endo-vinyl-exo-aryl vinylcarbonyl ylides 17a-c arising from 2a-c undergo disrotatory cylization to exclusively produce 5, whereas the ylides 17d,e arising from 2d,e undergo partly symmetry-forbidden conrotaory cyclization to sterically stable trans-diaryldihydrofurans 6d,e as well as the symmetry-allowed process to 5d,e.

REACTION OF VINYLCARBENOIDS WITH CYCLIC DISULFIDES : FORMATION OF 1,3-INSERTION PRODUCTS AS WELL AS 1,1-INSERTION PRODUCTS

Abstract Reactions of vinylcarbenoids with cyclic disulfides were carried out. Rh 2 (OAc) 4 -catalyzed reaction of vinyldiazo compounds 1a-c with biphenylene disulfide 6 gave 1,3-insertion adducts 7a-c as the sole products in very good yields, while the reaction with dithiaphenanthrene 9 afforded only 1,1-insertion adducts 10a-c .

Reaction of vinylcarbenoids with thioketones: formation of vinylthiocarbonyl ylides followed by ring closure to thiiranes and dihydrothiophenes

Abstract Reactions were carried out on thioketones with vinylcarbenoids. Rh 2 (OAc) 4 -catalyzed reaction of vinyldiazo compounds 1a,b with xanthione 2 and thiochromone 3 gave thiiranes 4b and olefins 5 and 6 , desulfurization products from thiiranes, while the reaction of 1c with 2 and 3 afforded dihydrothiophenes 7, 8 and 9 .

Surprising 1,7-cyclization of vinyl carbonyl ylides generated from reaction of indanetrione with vinyl diazo compounds

Reactions of tricarbonyl compounds with vinyl diazo compounds 2 were carried out. Reaction of 1,2,3-indanetrione with 2a , b , c gave the spiroindan-1,3-dione-2,2′-benzodihydrooxepin 7a , b , c , but not normal products oxirane and dihydrofuran derivatives expected from intermediate vinyl carbonyl ylides 4 . Formation of 7 requires isomerization of vinyl carbonyl ylides 4 bearing a ( Z )-cyanostyryl group to unstable ( E )-form 5 and subsequent cyclization to oxepin 6 followed by a 1,5-hydrogen shift. However, reaction of 2 with six-membered cyclic tricarbonyl compounds 1,2,3-trioxo-2,3-dihydrophenalene 11 and dimethylalloxane 13 gave the dioxole 12 and the dihydrofuran 14 , respectively, typical products expected from vinyl carbonyl ylides.

Migration of double bond in decomposition of methylenepyrazoline

Abstract Thermal decomposition of 4-methylenepyazolines bearing an electron-withdrawing group at C-3 results in the formation of methylenecyclopropanes derived from migration of the double bond with the breaking of the CN bond.

Solvent effect on product distribution in the thermolysis of dihydropyrazoles

Solvent dependence of products in the thermal decomposition of 4-methoxy-4,5-dihydro-3H-pyrazoles bearing two electronegative groups at C-3 was observed; nonpolar solvents gave predominantly alkenes, whereas polar solvents gave predominantly cyclopropanes.

1,3-Polar addition of 1,3-oxazolium-4-olates with protic reagents

1,3-Oxazolium-4-olates react with water and alcohols to give 1,3-polar adducts, 1,3-oxazolidin-4-one derivatives, which, with water, undergo ring opening in two ways depending on the structure of the adduct.

On the structure of 1 : 1 adducts of mesoionic compounds with isocyanates

The reactions of the mesoionic species (1) with isocyanates yield the acylated mesoionic derivatives, formed via unstable cycloadducts, with thioisocyanates, reacting similarly; the products of reactions between other similar mesoionic systems and isocyanates, previously described as cycloadducts, are also shown to be acylated mesoionic compounds on the basis of their physical data.

1,3-Dipolar cycloaddition of mesoionic anhydro-4-hydroxy-1,3-dioxolium hydroxides with olefinic dipolarophiles

Stable cycloadducts between mesoionic compounds containing a lactone moiety and olefinic dipolarophiles were isolated for the first time mesoionic 1,3-dioxolium-4-oxides, generated in situ by the intramolecular carbone–carbonyl reaction of α-diazo-acetic benzoic and -bis(acetic) anhydrides.