Leo A. Paquette

Bio: Leo A. Paquette is an academic researcher from Ohio State University. The author has contributed to research in topics: Ring (chemistry) & Total synthesis. The author has an hindex of 36, co-authored 484 publications receiving 6021 citations. Previous affiliations of Leo A. Paquette include Heidelberg University.

Analysis of the Conformational Nature, Resolvability, and Thermal Racemization of Hetero 2,3-Dispiro Cyclohexanones. The Weighting of Carbonyl/C-X Stabilization Relative to the Electronic Interaction between the Vicinal Electronegative Substituents

Abstract: A series of hetero 2,3-dispiro cyclohexanones has been prepared. The conformations of the syn and anti isomers were assessed in the solid state, in solution, and in the gas phase (the latter by molecular mechanics calculations). The results are discussed in the light of steric, dipole, and gauche interactions; steric contributions give evidence of controlling ΔG eq . On a different front, the syn/anti pairs were found to interconvert when heated in the presence of a catalytic amount of acid. Three representative examples of these chiral molecules were resolved and complete racemization was observed to result under the conditions of equilibration

meso- and dl-Bivalvane (pentasecododecahedrane). Enantiomer recognition during reductive coupling of racemic and chiral 2,3-dihydro- and hexahydrotriquinacen-2-ones

Abstract: Pinacolic reduction of both optically pure and racemic hexahydrotriquinacen-2-one ( 6 ) proceeds with exo,exo carbon-carbon bond formation. Coupling of enantiomerically pure 6 produces diol 11 exclusively. Formation of comparable amounts of 11 and 12 from ( f ) 6 shows that the diastereomeric transition states involved are of comparable energy. Studies with chiral and racemic 2,3-dihydrotriquinacen-2-one (13) gave analogous results. The various 1,2-glycols are identified by their I3C N M R (symmetry is thereby revealed), ‘H NMR (shielding of the endo protons at Cj and C3, by hydroxyl is witnessed), and ir spectra, in tandem with the method of synthesis. Conversion of the four diols to their thionocarbonates, and subsequent treatment with triethyl phosphite at the reflux temperature, provides the structurally related olefins stereospecifically. Catalytic hydrogenation of 17 provides dl-bivalvane (2), whereas reduction of 19 gives rise to the meso-bivalvane isomer 3. Other aspects of these transformations and conformational possibilities for 2 and 3 are discussed. The dodecahedron is one of the five perfect solids (the others are the tetrahedron, cube, octahedron, and icosahedron) and consequently has been a source of fascination for mathematicians since the time of Pythagoras and Plato. Only recently, however, has the dodecahedrane molecule attracted the attention of synthetic chemists. Notwithstanding, this (CH)2o polyhedron, which is endowed with most intriguing geometry, remains an unknown Although several approaches to dodecahedrane are currently under investigation in these laboratories, attention is focused specifically herein on the fundamental aspects of that scheme which involves effective “dimerization” of two triquinacene halves. The essence of,this concept is not new, it having been advanced earlier in singular form by Woodward, Fukunaga, and Kelly2 who viewed dodecahedrane as composed of two triquinacene subunits which when properly arranged might be coaxed into sixfold carbon-carbon bond formation as illustrated in 1. That efforts along this

Tandem Development of Aqueous Indium Chemistry and Ring‐Closing Metathesis as a General Route to Fused‐Ring α‐Methylene‐γ‐butyrolactones

Abstract: A program directed toward a general synthesis of α-methylenelactones cis- or trans-fused to larger rings is reported. The protocol originates with two ω-unsaturated aldehydes of the same or different chain length. One of these is initially transformed by way of the Baylis–Hillman reaction into a functionalized allylic bromide. Merger of the two building blocks is subsequently accomplished in aqueous solution with powdered indium metal serving as the initiator. Once the lactone ring is crafted, the end products are generated by application of ring-closing metathesis. The central issues surrounding this final step are the effects of the stereochemical disposition of the side chains, the consequences of ring strain, and the locus of the double bonds on cyclization efficiency.

C-H bond functionalization: emerging synthetic tools for natural products and pharmaceuticals

Abstract: The direct functionalization of C-H bonds in organic compounds has recently emerged as a powerful and ideal method for the formation of carbon-carbon and carbon-heteroatom bonds. This Review provides an overview of C-H bond functionalization strategies for the rapid synthesis of biologically active compounds such as natural products and pharmaceutical targets.

Palladium-catalyzed cross-coupling reactions in total synthesis.

Abstract: In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

Organic Reactions in Aqueous Media with a Focus on Carbon−Carbon Bond Formations: A Decade Update

Abstract: 4.2.8. Reductive Coupling 3109 5. Reaction of Aromatic Compounds 3110 5.1. Electrophilic Substitutions 3110 5.2. Radical Substitution 3111 5.3. Oxidative Coupling 3111 5.4. Photochemical Reactions 3111 6. Reaction of Carbonyl Compounds 3111 6.1. Nucleophilic Additions 3111 6.1.1. Allylation 3111 6.1.2. Propargylation 3120 6.1.3. Benzylation 3121 6.1.4. Arylation/Vinylation 3121 6.1.5. Alkynylation 3121 6.1.6. Alkylation 3121 6.1.7. Reformatsky-Type Reaction 3122 6.1.8. Direct Aldol Reaction 3122 6.1.9. Mukaiyama Aldol Reaction 3124 6.1.10. Hydrogen Cyanide Addition 3125 6.2. Pinacol Coupling 3126 6.3. Wittig Reactions 3126 7. Reaction of R,â-Unsaturated Carbonyl Compounds 3127

Cascade reactions in total synthesis.

Abstract: The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.