 | Samantha Espinosa College of Saint Elizabeth ChemistryMentor(s)Lawrence Williams, PhD. Rojita Sharma, B.S. Department of Chemistry and Chemical Biology Rutgers University |
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| Direct Allene Synthesis | ||
| Here we present a simple, convenient, single flask synthesis of allenes from inexpensive commercial materials. In contrast to alkenes and alkynes, allenes are stereogenic and span three carbons and offer unique structural scaffolds and opportunities for chemical synthesis. Although many diverse alkenes and alkynes are available, few allenes can be obtained from commercial sources. For example, Sigma-Aldrich, one of the most widely used chemical supply companies, offers 67 alkenes and 88 alkynes but only 5 allenes. Normally, allene synthesis requires many separate reactions and the isolation and purification of many intermediates. Our approach focused on a multiple component reaction sequence to prepare allenes by sequential addition of reagents. Specifically, combination of alkynylides with aldehydes, exposure to methane sulfonyl chloride, and then transfer to a suitable cuprate reagent solution gave allenes directly. Importantly, alkynylides are available and used directly from combination of commercial alkynes and base; a wide range of aldehydes is commercially available, as is methane sulfonyl chloride. Cuprates are easily prepared in situ from commercial reagents as well. Moreover, we found a recently described copper hydride source can be used in this procedure to prepare mono-, di-, and tri-subsituted allenes with high stereoselectivity. The yields of allene synthesized by our method are high (80-90%). For example, nona-3, 4-dienylbenzene was obtained in 79% yield by alkynylation of hydrocinnamaldehyde and 1-hexyne with n-butyl lithium as base, followed by mesylation, and then treatment with copper hydride on 22 mg scale. This method should facilitate the study and use of allenes. |