The orthogonal arrangement of cumulated double bonds has attracted a great deal of attention from the scientific community since the first allene was prepared by Burton and von Pechmann in 1887. [1] The selection of substituents having a different electronic nature allows the ambivalent reactivity of allenes towards nucleophilic as well as electrophilic reagents with controlled regio-and stereoselectivity. [2,3] Thus, donor/acceptor-substituted allenes have emerged among the most versatile synthetic building blocks in the development of novel carbon-carbon bond-forming reactions (Scheme 1). In contrast, the reactivity behavior of [n]cumulene derivatives, compounds with three or more consecutive double bonds, has not been fully explored because of the difficulty associated with their preparation other than tetrasubstituted [3]cumulene derivatives. [4] While a limited number of acyl-substituted [3]cumulene derivatives are known to be stable [5] and subsequently utilized in the enyne cycloaddition, [6] palladium-catalyzed arylation, [7] Lewis acid catalyzed Diels-Alder reactions, [8] phosphine- [9] and silvercatalyzed [3+2] cycloaddition reactions, [10] the synthesis as well as synthetic utility of donor-substituted [3]cumulene derivatives have yet to be established. [11] Recently, we reported a facile a-vinyl enolization pathway of (E)-b-chlorovinyl ketones in which transient oxy-substituted [3]cumulene derivatives [i.e., cumulenol(ate)s] were postulated as nucleophilic species, reacting either with a protic source [12] or aldehydes [13] (Scheme 2). Drawn by the possibility of investigating the ambivalent reactivity modes of donor-substituted [3]cumulene derivatives, we envisioned a reaction of in situ generated [3]cumulene derivatives with nucleophiles. Herein, we report an electrophilic reactivity mode of oxy-substituted [3]cumulene derivatives in the syntheses of vinyl allenones and 3-methylenepyrrolidines with excellent stereoselectivities.During the course of our investigation into the nucleophilicity of b-chlorovinyl ketones, we observed the formation of the aldol product 2 a as well as the vinyl allenone 3 a under the influence of lithium salts (Table 1). [13] While 3 a was obtained with a low yield of 15 %, we were particularly encouraged by the fact that 3 a, a trisubstituted alkene, was formed stereoselectively. To optimize the formation of 3 a, we Scheme 1. Known and proposed reactivity patterns of functionalized allenes and [3]cumulenes. Scheme 2. Ambivalent reactivity modes of in situ generated oxy-substituted [3]cumulenes.
Scheme 1. Known and proposed reactivity patterns of functionalized allenes and [3]cumulenes. Scheme 2. Ambivalent reactivity modes of in situ generated oxy-substituted [3]cumulenes.
Crosslinked polymers have a covalent bridge that connects two polymer strands at multiple points, creating a network or matrix that is very robust. These types of polymers may either be stable indefinitely, or degrade over time; those that degrade over time typically do so at a constant rate. What is not available currently is a polymer that is stable indefinitely, but then can be degraded on command. Being able to create an adhesive that could undergo de-bonding on command would be very useful. We have designed an electrochemically degradable crosslinking reagent (EDCR) composed of a bi-functional polymer crosslinking moiety and an electroactive core that undergoes degradation under reductive conditions. The EDCR is composed of a quinone center with two terminal amines attached. This crosslinker will be used to make a reversible epoxy adhesive. Epoxys are two-component adhesives that consist of a crosslinking amine hardener and an epoxide-containing polymer resin. Mixing of these components leads to a reaction between the epoxy groups and the terminal amines on the hardener. This work shows the construction of a protected form of an EDCR. Once deprotected, it should work as a hardener that will be stable indefinitely, but will degrade with the application of a low voltage current. v ACKNOWLEDGEMENTS I would like to start by thanking my research advisor Marc d'Alarcao for being there for me throughout my time at SJSU. I have learned more from Prof. d'Alarcao than any other professor; I have learned to look at problems more critically and logically. I cannot thank him enough for all the ways he has helped me with my research, in addition to becoming a better chemist. He has also been there anytime I have needed advice outside of chemistry. Prof. d'Alarcao has been more than understanding and helpful when it came to raising my son while making my way through the master's program. I would also like to thank my committee members Prof. Roger Terrill and Prof. David Brook for taking time out of their schedule to be on my committee and help better my thesis work. I would like to thank Dr. Melody Esfandiari who has made me a better teacher and helped me significantly in my writing skills. I could not have made it though this master's program as easily without the help of my friends, fellow graduate students and TA's Tony Pan, John Kim, Jamie Lunkley, Victoria Chang, Thanh Ngoc-Le, and Tim Hom, without whom I would have been lost my first years teaching and my time would not have been as enjoyable at SJSU. I would like to thank my lab mates in the d'Alarcao lab who made the late nights entertaining. Lastly, I am most grateful for my son Jaxon Meury, who has been my biggest motivation for doing my best while at SJSU. And of course my parents for being extraordinarily supportive of me in so many ways while out here in California. vi
Treatment of β‐chlorovinyl ketones with NEt3 and LiClO4 or LiBr results in formation of electrophilic lithium cumulenolates which smoothly react with nucleophiles such as another cumulenolate or ketimines to afford vinyl allenones like (II) or pyrrolidines of type (IV)/(VII) in a stereoselective manner.
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