95123-96-9Relevant academic research and scientific papers
Tandem ring-opening/ring-closing metathesis polymerization: Relationship between monomer structure and reactivity
Park, Hyeon,Lee, Ho-Keun,Choi, Tae-Lim
supporting information, p. 10769 - 10775 (2013/08/23)
Monomers containing either cycloalkenes with low ring strain or 1-alkynes are poor monomers for olefin metathesis polymerization. Ironically, keeping two inactive functional groups in proximity within one molecule can make it an excellent monomer for metathesis polymerization. Recently, we demonstrated that monomer 1 having cyclohexene and propargyl moieties underwent rapid tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization via relay-type mechanism. Furthermore, living polymerization was achieved when a third-generation Grubbs catalyst was used. Here, we present a full account on this tandem polymerization by investigating how various structural modifications of the monomers affected the reactivity of the tandem polymerization. We observed that changing the ring size of the cycloalkene moieties, the length of the alkynes, and linker units influenced not only the polymerization rates but also the reactivities of Diels-Alder reaction, which is a post-modification reaction of the resulting polymers. Also, the mechanism of tandem polymerization was studied by conducting end-group analysis using 1H NMR analysis, thereby concluding that the polymerization occurred by the alkyne-first pathway. With this mechanistic conclusion, factors responsible for the dramatic structure-reactivity relationship were proposed. Lastly, tandem RO/RCM polymerization of monomers containing sterically challenging trisubstituted cycloalkenes was successfully carried out to give polymer repeat units having tetrasubstituted cycloalkenes.
Annulation via alkylation - Alder ene cyclizations. Pd-catalyzed cycloisomerization of 1,6-enynes
Trost, Barry M.,Lautens,Chan,Jebaratnam,Mueller
, p. 636 - 644 (2007/10/02)
A Pd(0)-catalyzed alkylation of an allyl substrate with a nucleophile containing a double or triple bond to permit subsequent thermal Alder ene reactions constitutes a novel annulation protocol. In the case of a triple bond, a Pd(2+) complex catalyzes an equivalent of an Alder ene reaction. This new cyclization is probed in terms of the effect of substitution on the olefin, the acetylene, and the tether connecting the two. The reaction produces both 1,4-dienes (Alder ene-type products) and 1,3-dienes. Mechanisms to account for the diversity of products are presented. The Pd(2+)-catalyzed reaction shows an ability to interact with remote nonreactive parts of substrates to affect conformation and thereby selectivity. Several advantages accrue to the Pd(2+)-catalyzed reaction. First, the reaction normally proceeds at temperatures between 25 and 65°C instead of the > 250°C (in static systems) to > 500°C (in flow systems) for the thermal reaction. Second, reactions that fail thermally succeed via the metal-catalyzed process. Third, complementary regioselectivity may be observed. Fourth, the ligating properties of the metal catalyst offer opportunities for exercising control not possible in a simple thermal process. A novel cyclopentannulation of allyl alcohols and related derivatives evolves in which Pd(0) catalyzes formation of the first bond and a simple electronic switch to Pd(2+) catalyzes formation of the second bond.
