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9.9.5.3.1 Synthesis by Elimination

DOI: 10.1055/sos-SD-109-00053

Hou, X. -L.; Peng, X. -S.; Yeung, K. -S.; Wong, H. N. C.Science of Synthesis Knowledge Updates, (20112336.

Furans can be synthesized via the reduction of furan-2(5H)-ones and subsequent elimination of water or methanol. For example, the furanone 229, shown in Scheme 110, is transformed into furan 230 through reduction with diisobutylaluminum hydride followed by dehydration using hydrochloric acid.[‌240‌‌242‌] The overall transformation can be achieved indirectly from β,γ-dihydroxy ketones by double dehydration under heating with a catalytic amount of an acid, as represented in Scheme 111.[‌243‌,‌244‌] Lewis acids, such as bromotrimethylsilane or trimethylsilyl trifluoromethanesulfonate, can also be employed to induce the elimination.[‌245‌] The eliminative aromatization that can occur in 2,5-dimethoxy-2,5-dihydrofuran has been exploited in a reaction with vinyl ethers to generate 2-substituted furans in modest yields.[‌246‌] The elimination step can also proceed through a 3-bromo-2,3-dihydrofuran intermediate during the aromatization of 4-(trichloroacetyl)-2,3-dihydrofuran to the corresponding furan product.[‌247‌]

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