A General Model for Selectivity in Olefin Cross Metathesis

Abstract

In recent years, olefin cross metathesis (CM) has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several classes of olefins, including substituted and functionalized styrenes, secondary allylic alcohols, tertiary allylic alcohols, and olefins with alpha-quaternary centers, have led to a general model useful for the prediction of product selectivity and stereoselectivity in cross metathesis. As a general ranking of olefin reactivity in CM, olefins can be categorized by their relative abilities to undergo homodimerization via cross metathesis and the susceptibility of their homodimers toward secondary metathesis reactions. When an olefin of high reactivity is reacted with an olefin of lower reactivity (sterically bulky, electron-deficient, etc.), selective cross metathesis can be achieved using feedstock stoichiometries as low as 1:1. By employing a metathesis catalyst with the appropriate activity, selective cross metathesis reactions can be achieved with a wide variety of electron-rich, electron-deficient, and sterically bulky olefins. Application of this model has allowed for the prediction and development of selective cross metathesis reactions, culminating in unprecedented three-component intermolecular cross metathesis reactions.

Ruthenium vinyl carbene intermediates in enyne metathesis

“…[72,74] Alkyne coordination and rearrangement to vinylidene V is followed by elimination of H 2 O to give allenylidene cation W. Addition of methanol to the electrophilic C α position will generate the observed vinyl carbenes 71 after proton transfer. (48) Similar reactivity profile is observed with the isocyanide ruthenium(II) complex in its reaction with a 1,3-enyne. In this example, the trimethylphosphine ligand of cationic complex 69 (Scheme 31, above) was replaced by t-butylisocyanide (eq 49).…”

“…Eventually, the loss of ethylene from the metal coordination sphere results in entropic driving force to give the cross alkene metathesis product. A full summary of Grubbs' mechanistic work [45][46][47] and a selectivity model for alkene metathesis [48] are available. The methylidene plays a critical role in alkene metathesis by linking catalytic cycles.…”

Arenicolides A−C, 26-Membered Ring Macrolides from the Marine Actinomycete Salinispora arenicola

“…Arenicolide B (2) eluted from the C 18 HPLC column prior to 1 (1 t R = 69 min; 2 t R = 55 min) and was assigned the molecular formula C 44 Table S1 for complete NMR data) established that 2 was the C-6 O-desmethyl isomer of arenicolide A, as indicated by loss of the corresponding methoxy singlet and the upfield shift of C-6 [δ C-6 75.7]. Analysis of the 2D NMR data conclusively established the gross structure as depicted for 2.…”

Concomitant Addition and Acetalization of α,β‐Unsaturated Aldehydes with Diols.

“…1 One of them seemed to be 2-vinyl-1,3-dioxolane (3a), which is a widely known compound, but its formation under the reaction conditions was totally unexpected. In order to confirm the identity of the compound we attempted preparation of authentic compound of 3a from acrolein (1a) and ethylene glycol (2). However, the preparation of 3a by direct acetalization of 1a with 2 was not straightforward.…”