- Double dehydro-diels-alder reactions of 1,5-dien-3-ynes
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A study was conducted to demonstrate double dehydro-diels-alder reactions of 1,5-dien-3-ynes. It was demonstrated that the reaction proceeded through two concerted cycloadditions, the first of which was proposed to be reversible. Detailed analysis reveale
- Fallon, Thomas,Robinson, Diane E.J.E.,Willis, Anthony C.,Paddon-Row, Michael N.,Sherburn, Michael S.
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supporting information; experimental part
p. 760 - 765
(2010/05/18)
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- Keto ethers. IV. Products formed on reaction of dihydro-2,2,5,5-tetramethyl-3(2H)-furanone with strong acids
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Reaction of tetrahydro-2,2,5,5-tetramethyl-3(2H)-furanone (1) with 96 or ca. 100percent sulfuric acid or hot polyphosphoric acid followed by aqueous quenching gave the following products: 2-hydroxy-2,5-dimethyl-4-hexen-3-one (3), 2,4,4-trimethyl-2-cyclopenten-1-one (7), 3,5,5-trimethyl-2-cyclopenten-1-one (8), tetrahydro-2,3,5,5-tetramethylfuran-2,3-diol (11), 2,5-dihydro-3,5,5-trimethyl-2-methylenefuran (17) and its dimer 20, 2,5-dihydro-2,3,5,5-tetramethyl-2-furanol (18), 4-hydroxy-2,4-dimethyl-2-pentenoic acid γ-lactone (22), 2,3,5-trimethyl-2-cyclopenten-1-one (23), and tetramethylfuran (25).In 96percent sulfuric acid the products arise by ring opening, ring opening followed by reclosure to carbocyclic products, methyl migration from C-2 to C-3 to give rearranged furan derivatives, and oxidation.In ca. 100percent sulfuric acid or hot polyphosphoric acid further methyl migrations can occur to give 23 and 25.
- Yates, Peter,Burke, Patrick Michael
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p. 1695 - 1704
(2007/10/02)
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- The Pyrolysis of 4-Alkylidene-3,3,5,5-tetramethyl-1-pyrazolines
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The pyrolysis of 4-alkylidene-3,3,5,5-tetramethyl-1-pyrazolines normally gives alkylidene-2,2,3,3-tetramethylcyclopropanes and at higher temperature or longer reaction times conjugated dienes .In some cases interesting variations occur.Foe example, 3,3,5,5-tetramethyl-1-pyrazolin-4-ylidenemalonitrile (22) gives (eventually) 3-cyano-4-isopropenyl-5-methylpyridine (27) and in the dichloro-substituted series a rearrangement from 2,2-dichloro-3,3-dimethylisopropylidenecyclopropane (30) to 3,4-dichloro-3,5-dimethylhexa-2,4-diene (31) and a double HCl elimination to give 2,5-dimethylhexa-1,5-dien-3-yne (32) are observed.The kinetics of nitrogen elimination have been determined for ten differently substituted pyrazolines (33).The reactions have positive entropies of activation and hence seems to pass through a singlet rather than (as suggested in analogous systems) a triplet intermediate but it is difficult to be sure whether this is a TMM biradical (simultaneous cleavage of both C-N bonds) or a diazenyl biradical (sequential cleavage of the C-N bonds).It is, however, interesting to note that there is no correlation between the reaction rate and the radical-stabilizing ability of the substituents X and Y on the alkylidene group.This, in turn, suggests little or no rotation of the CMe2 groups at the transition state and possibly the formation of a bis-orthogonal TMM (47) or a monoorthogonal diazenyl biradical (48).
- Bushby, Richard J.,Jesudason, Malini V.,Pollard, Michael D.
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p. 2655 - 2662
(2007/10/02)
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