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Vinylogous ene reaction

Ene reactions are promoted by titanium compounds as Lewis acids [405-409]. The carbonyl ene reaction of methylenedihydrofuran with aldehyde (Eq. 161) [410] and intramolecular reaction of an unsaturated aldehyde (Eq. 162) [411] are illustrated below. The cyclization of a conjugated ketone in the presence of a mixture of TiCU and Ti(0-/-Pr)4, as shown in Eq. (163), cleanly afforded the bicyclic ketone this might be considered as the product of a vinylogous ene reaction [412]. [Pg.720]

As a model substrate, 2,5-dimethyl-2,4-hexadiene 51 has been intensively investigated by several research groups. Depending on the solvent polarity, hve peroxidic products have been isolated in varying relative yields the endoperoxide 52 (from [4 + 2]-cycloaddition), the aUylic hydroperoxide 53 (from ene reaction), the 1,2-dioxetane 54 (from [2 + 2]-cycloaddition), the diene hydroperoxide 55 (either from a vinylogous ene reaction or a radical-induced rearrangement of 53), and the methoxy-substituted hydroperoxide 56 (a methanol trapping product) were observed. A maximum of 23% of the [4 -I- 2]-cycloaddition product 52 was detected in tetrachloromethane, whereas the dioxetane 54 dominated in polar acetonitrile. [Pg.514]

GoUnick, K. and Griesbeck, A., Interactions of singlet oxygen with 2,5-dimethyl-2,4-hexadiene in polar and non-polar solvents. Evidence for a vinylog ene-reaction. Tetrahedron, 40, 3235,1984. [Pg.520]

Scheme 27 Vinylogous Mannich reaction of silyl dienolates 2.3.5 Aza-Ene-Type Reaction... Scheme 27 Vinylogous Mannich reaction of silyl dienolates 2.3.5 Aza-Ene-Type Reaction...
BINOL-Ti catalysis is also applicable to carbonyl-ene reaction with formaldehyde or vinylogous and alkynylogous analogs of glyoxylates in the catalytic desymmetrization (vide infra) approach to the asymmetric synthesis of isocarbacycline analogs (Scheme 8C.7) [24],... [Pg.546]

Nussbaumer and Frdter have used a vinylogous carbonate as an enophile. Pyrolysis of a solution of (126) in toluene at 3(X) C for 9 h gives (127), an intermediate in a synthesis of CM-7-irone, in 25% yield as the only cyclization product. Acid-catalyzed cyclization of (126) gives only the isomer of (127) with an endocyclic double bond. Thomas and Lander-Schouwey found that pyrolysis of (128) in decalin at 3(X) C results in a retro-ene reaction to give propene and (129) which undergoes an intramolecular ene reaction to give (130). ... [Pg.19]

The ester/alkyne rearrangement system can be extended by conjugation to involve a more distant site. The reaction of diethyl phosphorochloridate with 3-methylhex-4-yne-2-ene-l-ol leads to the vinylogous propargylic ester rearrangement as shown in Equation 4.39.176... [Pg.131]

A quantitative solid-state ene addition between two ligands of the platinum complex 397 gives the rearranged platinum complex 398 upon extensive heating to 140 °C [123]. This rearrangement reaction (cf. Sect. 24) is treated here, as it is the only known quantitative solid-state ene addition to date. Further quantitative solid-state [4-1-4] additions and higher vinylogs, as well as ene additions also of the intermolecular type, await detection both as thermal and photochemical reactions. [Pg.168]

The 2-substituted l,3-thiazin-6-thiones 33 and 34 and 160 and 161 are accessible by reacting 3,3-dichloroprop-2-ene iminium salts (vinylogous Viehe salts) with thiobenzamide or WA -disubstituted thioureas (Scheme 11) <1997S573>. The ring closure occurs with loss of amine as the hydrochloride salt and the thiones are generated after a reaction with another thioamide molecule. [Pg.585]

Irradiation of vinylogous imides 56 and 58 led to products derived from a different reaction pathway. None of the expected [2 + 2] adducts formed, but instead products 57 and 59 resulting from a photochemical ene-type reaction were isolated in good yield (Scheme 15)35. The authors proposed that hydrogen atom transfer from diradical 60 could lead to the formation of the observed product 57. [Pg.653]

The enantioselective gold(I)-catalysed vinylogous 3 + 2-cycloaddition reaction between vinyldiazoacetate and 4-substituted l-(methoxymethylene)cyclohexane furnished substituted spiro[4.5]dec-2-enes in high yields (70%), high diastereoselectivity (>30 1 dr), and high enantioselectivity (70% ee). A gold vinylcarbene is a key intermediate in this reaction. (5 ... [Pg.489]


See other pages where Vinylogous ene reaction is mentioned: [Pg.710]    [Pg.184]    [Pg.2224]    [Pg.2224]    [Pg.710]    [Pg.184]    [Pg.2224]    [Pg.2224]    [Pg.109]    [Pg.25]    [Pg.291]    [Pg.69]    [Pg.107]    [Pg.581]    [Pg.143]    [Pg.344]    [Pg.575]    [Pg.318]    [Pg.291]    [Pg.591]    [Pg.464]    [Pg.174]    [Pg.163]   
See also in sourсe #XX -- [ Pg.720 ]




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