Showing papers by "Leo A. Paquette published in 1991"
TL;DR: In this article, the triisobutylaluminum-catalyzed Claisen rearrangement of a series of bicyclic allyl vinyl ethers was examined in connection with a planned synthesis of the diterpene epoxydictymene.
Abstract: The triisobutylaluminum-catalyzed Claisen rearrangement of a series of bicyclic allyl vinyl ethers was examined in connection with a planned synthesis of the diterpene epoxydictymene. The exocyclic vinyl ethers studied undergo [3,3] sigmatropy via chairlike transition states to provide products having Z stereochemistry about the double bond of the eight-membered ring. Differences appear only in the extent of stereoselectivity in the ensuing carbonyl reduction step. Two companion endocyclic vinyl ethers were found to utilize boat transition states to deliver Z products exclusively. In all cases, the level of chirality transfer is excellent
49 citations
TL;DR: In this paper, the authors examined the atropisomerism of tricyclic E, syn, up enolates derived from anionic oxy-Cope rearrangement of 1-vinyl-2-cyclohexenyl-7,7-dimethyl-exo-norbornan-2 -ols.
Abstract: The phenomenon of atropisomerism is critically examined in the tricyclic E, syn, up enolates derived from anionic oxy-Cope rearrangement of 1-vinyl-2-cyclohexenyl-7,7-dimethyl-exo-norbornan-2-ols, as well as the ketones derived from their protonation and methylation. In all cases studied, the [3,3] sigmatropic shift proceeds with 100% stereoselectivity via the endo-chair transition-state option. The E and syn stereochemistry is established during chirality transfer at this stage. The «oxygen-up» conformation stems directly from the structural features inherent in the starting alcohols. In the unsubstituted example and with certain substitution pattrerns in the original cyclohexene ring, the E, syn, up enolates are seen to be thermodynamically unstable relative to their E, syn, down atropisomers, such that products results exclusively by electrophilic capture of the latter. By suitable substitution, the barrier to this preequilibrium can be sufficiently heightened so that products resulting from the E, syn, up species can be obtained
42 citations
TL;DR: In this paper, the authors compose du titre a partir d'5-isopropyl-2-methylcyclopent-1-ene carbaldehyde via the transposition Claisen d'un derive de cyclopenta pyrane en derive decyclopenta cyclooctene.
Abstract: Synthese du compose du titre a partir d'5-isopropyl-2-methylcyclopent-1-ene carbaldehyde via la transposition Claisen d'un derive de cyclopenta pyrane en derive de cyclopenta cyclooctene
42 citations
TL;DR: In this paper, the trispiro isomers 3-5 and 4-5 were investigated and their solid-state conformational properties were compared to those of their lower homologues 6 and 7.
Abstract: We have initially developed methodology amenable to the convenient preparation of the trispiro isomers 3-5 shown herein and have elucidated their solid-state conformational features. Furthermore, the binding properties of 3-5 have been compared to those of their previously unknown lower homologues 6 and 7
27 citations
20 citations
15 citations
12 citations
TL;DR: In this paper, a sequence was developed for enhancing the level of functionality in both of these sectors within the central medium-sized ring without incurring ring closure, as a consequence of the close proximity of the olefinic and carbonyl centers in ketone 4.
Abstract: As a consequence of the close proximity of the olefinic and carbonyl centers in ketone 4, the molecule participates readily in transannular reactions. Sequences have been developed for enhancing the level of functionality in both of these sectors within the central medium-sized ring without incurring ring closure
11 citations
TL;DR: In this article, the reversibility of the thermal oxy-Cope rearrangement is demonstrated with the specific example, and the pathway and energetics associated with this phenomenon are outlined.
10 citations
TL;DR: In this article, a concise route from dihydropyran to the furans 12 and 13 has been developed that takes advantage of the regioselective Baeyer-Villiger oxidation of bicyclic ketone 6.
8 citations
TL;DR: The conjoining of two dodecahedryl units in a para relationship on a benzene ring has also been realized as discussed by the authors, which is a useful precursor of epoxydodecahedrane.
TL;DR: A total synthesis of (±)-hirsutene has been achieved in 9 steps and 14% overall yield via a twofold cycloadditive scheme that utilizes 4,4-dimethylcyclopentene, 1-(trimethylsilyloxy)butadiene, and ethylene as the three key building blocks.
Abstract: A total synthesis of (±)-hirsutene has been achieved in 9 steps and in 14% overall yield via a twofold cycloadditive scheme that utilizes 4,4-dimethylcyclopentene, 1-(trimethylsilyloxy)butadiene, and ethylene as the three key building blocks.
TL;DR: The enolate anions of 5-norbornen-2-one and 2 -norbornanone enter into self-coupling with their conjugate acids in a manner that exhibits diastereomeric discrimination as discussed by the authors.
Abstract: The enolate anions of 5-norbornen-2-one and 2-norbornanone enter into self-coupling with their conjugate acids in a manner that exhibits diastereomeric discrimination. The major products obtained from aldol reactions conducted at low temperature are those where bonding has occurred preferentially to the ketone of like absolute configuration. When the reactions are effected at higher temperatures, dehydration also occurs spontaneously. All indicators point to adherence by these bicyclic systems to molecular recognition in these condensation reactions as well. The aldol products, which are stable to the conditions under which they are formed, have been evaluated for their inherent levels of total energy and strain energy by molecular mechanics methods
TL;DR: The feasibility of generating the anion of dodecahedrane by direct metalation, reductive lithiation with aromatic radical anions, and by transmetalation with alkyllithiums has been examined as mentioned in this paper.
TL;DR: In this paper, various functionalized derivatives of trans-2,6-dimethylcyclooct-5-enol have been prepared and found to be recalcitrant to free radical or ionic six-ring cyclization with formation of a new carbon-carbon bond syn to the original hydroxy group at the pro-quaternary site.
Abstract: Various functionalized derivatives of trans-2,6-dimethylcyclooct-5-enol have been prepared and found to be recalcitrant to free radical or ionic six-ring cyclization with formation of a new carbon–carbon bond syn to the original hydroxy group at the pro-quaternary site. However, intramolecular syn delivery was achieved with complete regiocontrol by epoxidation/ring opening of the MOM ether, oxidation to the α,β-unsaturated ketone 35a, RhI-catalysed hydrosilylation to give 36, and exposure of this silyl enol ether to stannic chloride in the presence of ‘proton sponge’. The pivotal ring closure leads in good yield to 32, thereby solving the problem posed by untoward kinetic barriers to ring closure that are present under alternative conditions.
TL;DR: A comparison of the molecular densities and packing coefficients of (I) [4]peristylane-1,5-dione with (II), indicates that the change in crystal density is the sole result of an increase in molecular density with NO2 substitution.
Abstract: Decahydro-1,6:3,4-dimethano-3a-nitrocyclobuta [1,2:3,4]dicyclopentene-2,5-dione (II), C12-H11NO4, Mr = 233.2, monoclinic, P2(1)/n, a = 13.378 (7), b = 6.614 (1), c = 23.040 (15) A, beta = 92.53 (5) degrees, V = 2036.6 (4) A3, Z = 8, D chi = 1.521 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 9.3 cm-1, F(000) = 1312, T = 293 K, final R = 0.047, wR = 0.075 for 3075 reflections with I greater than 3 sigma(I). There are no unusually short intermolecular distances. A comparison of the molecular densities and packing coefficients of (I) [4]peristylane-1,5-dione with (II), indicates that the change in crystal density from (I) (1.415 g cm-3) to (II) (1.521 g cm-3) is the sole result of an increase in molecular density with NO2 substitution. The packing coefficients for (I) and (II) are identical.
TL;DR: In this paper, the triisobutylaluminum-catalyzed Claisen rearrangement of a series of bicyclic allyl vinyl ethers was examined in connection with a planned synthesis of the diterpene epoxydictymene.
Abstract: The triisobutylaluminum-catalyzed Claisen rearrangement of a series of bicyclic allyl vinyl ethers was examined in connection with a planned synthesis of the diterpene epoxydictymene. The exocyclic vinyl ethers studied undergo [3,3] sigmatropy via chairlike transition states to provide products having Z stereochemistry about the double bond of the eight-membered ring. Differences appear only in the extent of stereoselectivity in the ensuing carbonyl reduction step. Two companion endocyclic vinyl ethers were found to utilize boat transition states to deliver Z products exclusively. In all cases, the level of chirality transfer is excellent
TL;DR: In this paper, a condensation des derives de (7,7-dimethylnorcar-2,en-3-yl trimethyl)stannane avec le 2-chlorocyclohexanone was presented.
Abstract: La condensation des derives de (7,7-dimethylnorcar-2-en-3-yl trimethyl)stannane avec le 2-chlorocyclohexanone donne des derives de (2-[7,7−dimethylnorcar-2-en-3-yl]-1-vinyl)cyclohexanol. Ces derives subissent ensuite differentes transpositions chimiques. On obtient des derives de tricyclopentadecene et de tetracyclopentadecene
TL;DR: The enolate anions of 5-norbornen-2-one and 2 -norbornanone enter into self-coupling with their conjugate acids in a manner that exhibits diastereomeric discrimination.
Abstract: The enolate anions of 5-norbornen-2-one and 2-norbornanone enter into self-coupling with their conjugate acids in a manner that exhibits diastereomeric discrimination. The major products obtained from aldol reactions conducted at low temperature are those where bonding has occurred preferentially to the ketone of like absolute configuration. When the reactions are effected at higher temperatures, dehydration also occurs spontaneously. All indicators point to adherence by these bicyclic systems to molecular recognition in these condensation reactions as well. The aldol products, which are stable to the conditions under which they are formed, have been evaluated for their inherent levels of total energy and strain energy by molecular mechanics methods
TL;DR: In this article, various functionalized derivatives of trans-2,6-dimethylcyclooct-5-enol have been prepared and found to be recalcitrant to free radical or ionic six-ring cyclization with formation of a new carbon-carbon bond syn to the original hydroxy group at the pro-quaternary site.
Abstract: Various functionalized derivatives of trans-2,6-dimethylcyclooct-5-enol have been prepared and found to be recalcitrant to free radical or ionic six-ring cyclization with formation of a new carbon–carbon bond syn to the original hydroxy group at the pro-quaternary site. However, intramolecular syn delivery was achieved with complete regiocontrol by epoxidation/ring opening of the MOM ether, oxidation to the α,β-unsaturated ketone 35a, RhI-catalysed hydrosilylation to give 36, and exposure of this silyl enol ether to stannic chloride in the presence of ‘proton sponge’. The pivotal ring closure leads in good yield to 32, thereby solving the problem posed by untoward kinetic barriers to ring closure that are present under alternative conditions.
Abstract: We have initially developed methodology amenable to the convenient preparation of the trispiro isomers 3-5 shown herein and have elucidated their solid-state conformational features. Furthermore, the binding properties of 3-5 have been compared to those of their previously unknown lower homologues 6 and 7
TL;DR: In this paper, the reversibility of the thermal oxy-Cope rearrangement is demonstrated with the specific example, and the pathway and energetics associated with this phenomenon are outlined.
Abstract: The reversibility of the thermal oxy-Cope rearrangement is demonstrated with the specific example , and the pathway and energetics associated with this phenomenon are outlined.
TL;DR: In this paper, a concise route from dihydropyran to the furans 12 and 13 has been developed that takes advantage of the regioselective Baeyer-Villiger oxidation of bicyclic ketone 6.
Abstract: A concise route from dihydropyran to the furans 12 and 13 has been developed that takes advantage of the regioselective Baeyer-Villiger oxidation of bicyclic ketone 6.
TL;DR: In this article, the authors examined the atropisomerism of tricyclic E, syn, up enolates derived from anionic oxy-Cope rearrangement of 1-vinyl-2-cyclohexenyl-7,7-dimethyl-exo-norbornan-2 -ols.
Abstract: The phenomenon of atropisomerism is critically examined in the tricyclic E, syn, up enolates derived from anionic oxy-Cope rearrangement of 1-vinyl-2-cyclohexenyl-7,7-dimethyl-exo-norbornan-2-ols, as well as the ketones derived from their protonation and methylation. In all cases studied, the [3,3] sigmatropic shift proceeds with 100% stereoselectivity via the endo-chair transition-state option. The E and syn stereochemistry is established during chirality transfer at this stage. The «oxygen-up» conformation stems directly from the structural features inherent in the starting alcohols. In the unsubstituted example and with certain substitution pattrerns in the original cyclohexene ring, the E, syn, up enolates are seen to be thermodynamically unstable relative to their E, syn, down atropisomers, such that products results exclusively by electrophilic capture of the latter. By suitable substitution, the barrier to this preequilibrium can be sufficiently heightened so that products resulting from the E, syn, up species can be obtained
TL;DR: In this paper, the authors compose du titre a partir d'5-isopropyl-2-methylcyclopent-1-ene carbaldehyde via the transposition Claisen d'un derive de cyclopenta pyrane en derive decyclopenta cyclooctene.
Abstract: Synthese du compose du titre a partir d'5-isopropyl-2-methylcyclopent-1-ene carbaldehyde via la transposition Claisen d'un derive de cyclopenta pyrane en derive de cyclopenta cyclooctene