Ramon Gomez Arrayas

Bio: Ramon Gomez Arrayas is an academic researcher from Emory University. The author has contributed to research in topics: Cycloaddition & Allylic rearrangement. The author has an hindex of 5, co-authored 11 publications receiving 125 citations.

New oxidative demetalation protocol for molybdenum π-complexes: Enantiocontrolled synthesis of unsaturated ketones and lactones

Abstract: An efficient and general oxidative demetalation of (η3-allyl)molybdenum complexes using pyridinium dichromate allows the introduction of a carbonyl group at an allylic terminus of the π-system. The...

η3-Pyranyl and η3-Pyridinyl Molybdenum π-Complexes as Chiral Scaffolds for the Enantioselective Construction of Substituted Oxa- and Aza[3.3.1]bicyclics: First Enantio- and Regiocontrolled [5+3] Cycloaddition Reactions

Abstract: The first Mo-mediated [5+3] cycloadditions are reported. 3-Substituted pyranyl and pyridinyl molybdenum π-complexes participate in enantiocontrolled [5+3] cycloadditions and provide a new and efficient synthetic approach to oxa- and aza[3.3.1]bicyclics of high enantiomeric purity. The reaction proceeds in good to excellent yields and with complete regio- and endo-selectivities; it diverts to a [2+3] cycloaddition pathway when 2-substituted heterocycle π-complexes are used. This methodology, coupled with a variety of general demetalation protocols, holds much promise in synthetic applications.

The Enantiomeric Scaffold Approach to Highly Functionalized 1-Oxadecalines: Enantio- and Regiocontrolled [4+2] Cycloadditions of 5-Alkenyl-η3-Pyranylmolybenum Complexes

Abstract: TpMo(CO)2(5-alkenyl-η-2,3,4-pyranyl) diene complexes function as excellent chiral scaffolds for the efficient regio- and enantiocontrolled synthesis of highly functionalized 1-oxadecaline derivatives through a novel transition metal-mediated Diels−Alder reaction. Very good to excellent yields and excellent levels of endo selectivity are obtained, and the reaction gives products with complete retention of enantiomeric purity when carried out with chiral, nonracemic scaffolds. A subtle structural modification on the diene (replacement of an H by a trans-CH3 group) leads to a complete change of regiochemistry, which is discussed from a mechanistic point of view. The role of the η3-coordinated TpMo(CO)2 moiety is also critical to the further functionalization of the [4 + 2] cycloadducts, as illustrated by the preparation of 20 variously functionalized 1-oxadecaline derivatives (>98% ee when carried out with high enantiopurity scaffolds).

From a chiral switch to a ligand portfolio for asymmetric catalysis.

Abstract: This Account is divided into two sections. In the first section, the development of an enantioselective manufacturing process for ( S)-metolachlor, the active ingredient of the grass herbicide Dual Magnum, is described. This is today’s largest application of asymmetric catalysis, and the Ir-Xyliphos hydrogenation catalyst achieves unprecedented 2 millions turnovers. The development started in 1982 and ended when the first production batch was run in November 1996. The strategies and approaches used for attaining the elusive goal are described, and the lessons learned are discussed. In the second section, the development and performance of a portfolio of chiral diphosphines for industrial asymmetric applications are described. Central to the portfolio is the idea of modular ligand families, i.e., diphosphines with the same backbone, where steric and electronic properties are easily tuned by the choice of the substituents at the phosphorous atoms.

Transition-metal-catalyzed cycloadditions for the synthesis of eight-membered carbocycles.

Abstract: Eight-membered carbocycles are found in a wide variety of natural products that exhibit a broad range of biological and medicinal activities (cf. the most potent anticancer drug, taxol). However, the synthesis of eight-membered carbocycles is quite challenging as traditional approaches are met with entropic and enthalpic penalties in the ring-forming transition states. These negative effects can be totally or partially avoided with the implementation of transition-metal-catalyzed/mediated cycloadditions. In this Focus Review, examples of elegant and efficient metal-catalyzed and some metal-mediated cycloadditions (including Ni- catalyzed [4+4] and Rh-catalyzed [4+2+2] and [5+2+1] reactions) are presented to illustrate this. Application of these cycloaddition reactions in total synthesis is also presented to show the significance of these reactions in addressing challenges in natural product synthesis.

Recent Advances in the Catalytic Cycloaddition of 1,n-Dipoles

Abstract: Dipolar cycloaddition is one of the most valuable methods for synthesizing various carbo- and heterocycles because multiple carbon–carbon and carbon–heteroatom bonds form in a single step. Thus, practical generation of new 1,n-dipoles and control of their reactivities are significant aspects of modern organic chemistry. Although it is quite challenging to handle short-lived 1,n-dipolar species, 1,n-dipolar cycloadditions have been impressively developed in recent years. Advancement of their catalytic abilities has occurred because a catalyst enables 1,n-dipole generation and enhances the selectivities of the cycloadducts. In this Perspective, recent achievements in catalytic cycloadditions of 1,n-dipoles to synthesize medium-sized carbo- and heterocyclic compounds are addressed. Mechanistic insights and their applications toward the synthesis of natural products are also discussed.