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Cyclobutenes, electrocyclic ring-opening

The cyclohexadiene-hexatriene system seems to be less complicated than the cyclobutene-butadiene system. Cyclohexadiene undergoes photochemical electrocyclic ring opening ... [Pg.775]

Compound 6 is a pivotal intermediate in Schreiber s synthesis. It was hoped that the conspicuous and strained bridgehead cyclobutene substructure in 6 would undergo a conrotatory electrocyclic ring opening upon thermolysis to give an isomeric 1,3-diene (8, Scheme 1). In the event, when a solution of cyclobutene 6 in toluene is confined to a sealed tube and heated to 180°C for 12 h, a stereoisomeric mixture of 1,3-dienes 7 and 8 is produced in an excellent yield of 95% (7 8 ca. 5 1). Finally, irradiation of the 5 1 mixture of cis-7 and trans-8, or of each independently, establishes a photostationary state in which the desired trans isomer 8 predominates (8 7 ca. 10 1). [Pg.335]

Table 13-1. Computed reaction barriers and isomer stabilities [kcal/mol] for the electrocyclic ring opening of cyclobutene (relative to cyclobutene 1, including zero-point vibrational contributions). Except for G2, the results were obtained using the 6-311+G(d,p) basis set. Table 13-1. Computed reaction barriers and isomer stabilities [kcal/mol] for the electrocyclic ring opening of cyclobutene (relative to cyclobutene 1, including zero-point vibrational contributions). Except for G2, the results were obtained using the 6-311+G(d,p) basis set.
The forerunner in the Co-catalyzed [2+2+2] cycloaddition domino processes was that identified by Vollhardt and colleagues [273], with their excellent synthesis of steroids. Reaction of 6/4-1 with [CpCo(CO)2] gave compound 6/4-3 with an aromatic ring B via the intermediate 6/4-2. In this process, trimerization of the three alkyne moieties first takes place, and this is followed by an electrocyclic ring opening of the formed cyclobutene to give o-quinodimethane. This then undergoes a Diels-Alder reaction to provide the steroid 6/4-3 (Scheme 6/4.1). [Pg.458]

We are also carrying out calculations 40) for the electrocyclic ring opening of cyclobutene (27) and bicyclobutane (28) to 1,3-butadiene (29). While.this work is not yet complete, we have established that 27 opens preferentially by... [Pg.24]

We break the C4-C6 bond, and we form C3-C8 and C4-C9. The formation of the latter two bonds and the fact that we re forming a cyclobutanone suggests a [2+2] cycloaddition between a ketene at C3=C4=0 and the C8=C9 n bond. We can generate the requisite C3=C4 n bond by electrocyclic ring opening of the cyclobutene ring in the S.M. [Pg.104]

Intermediates (6) can yield to the corresponding [3-lactams via conrotatory electrocyclic closures (Fig. 3). The main features of these transition structures closely resemble those found for the thermal electrocyclic ring opening of cyclobutenes [34]. [Pg.318]

Consider the electrocyclic ring-opening reaction of cyclobutene. The molecule is formally divided into two fragments the double bond and the single 0 bond which is cleaved.9 The frontier orbital interactions (0,7t ) and (0, it) relevant to the conrota-tory and disrotatory reactions are given in diagrams 4, 5, 6 and 7, respectively. The net overlap is positive for 4 and 5, but zero for 6 and 7. The conrotatory process is therefore allowed, and the disrotatory process forbidden. [Pg.68]

Fig. 1. Transition structure for the electrocyclic ring opening of cyclobutene to rrans-l,3-butadiene... Fig. 1. Transition structure for the electrocyclic ring opening of cyclobutene to rrans-l,3-butadiene...
Table 1. Transition structure geometries, activation energies, and reaction energies for transition structures of electrocyclic ring opening of cyclobutene... [Pg.4]


See other pages where Cyclobutenes, electrocyclic ring-opening is mentioned: [Pg.300]    [Pg.229]    [Pg.300]    [Pg.229]    [Pg.923]    [Pg.515]    [Pg.44]    [Pg.255]    [Pg.255]    [Pg.255]    [Pg.486]    [Pg.24]    [Pg.89]    [Pg.343]    [Pg.343]    [Pg.375]    [Pg.375]    [Pg.253]    [Pg.254]    [Pg.923]    [Pg.1012]    [Pg.572]    [Pg.530]    [Pg.530]    [Pg.267]    [Pg.241]    [Pg.241]    [Pg.241]    [Pg.830]    [Pg.3]    [Pg.5]    [Pg.16]    [Pg.267]   
See also in sourсe #XX -- [ Pg.1030 ]

See also in sourсe #XX -- [ Pg.1030 ]

See also in sourсe #XX -- [ Pg.254 , Pg.273 , Pg.287 , Pg.354 ]

See also in sourсe #XX -- [ Pg.892 ]




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Cyclobutene

Cyclobutene derivatives, electrocyclic ring opening

Cyclobutene electrocyclization

Cyclobutene ring

Cyclobutene, ring opening

Cyclobutenes

Cyclobutenes opening

Cyclobutenes ring opening

Electrocyclic Ring Opening of Cyclobutene

Electrocyclic cyclobutene ring opening

Electrocyclic cyclobutene ring opening

Ring electrocyclic

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