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Escher, I.; Glorius, F., Science of Synthesis, (2007) 25, 758.
3-Halopropenals, which are readily available by the Vilsmeier–Haack–Arnold reaction (see Section 25.8.2.1.4.1), are valuable building blocks in transition-metal-catalyzed cross-coupling reactions (Scheme 33). For example, palladium-catalyzed cross-coupling of a variety of arylboronic acids with 3-chloropropenals can be carried out in aqueous media, to give 2-enals such as 1-(2-methoxyphenyl)-3,4-dihydronaphthalene-2-carbaldehyde (67),[177] in yields that are normally good to excellent. Trialkylated alkynylstannanes react by palladium-catalyzed cross-coupling reactions with 3-iodopropenals to give alkynylated enals 68, as do the corresponding alkynylsilanes. Purification of the products is more difficult in those reactions that use trialkylated alkynylstannanes, while the alkynylsilanes are less-reactive, and need to be activated with tetrabutylammonium fluoride prior to their use in the coupling step.[178,179] Simple terminal alkynes also undergo palladium-catalyzed cross-coupling with 3-bromopropenals under Sonogashira reaction conditions to afford alkynylated enals 69.[180] 1-Halo-2-nitroarenes may also be successfully cross-coupled with α-halogenated enals in a palladium-catalyzed Ullmann cross-coupling reaction. Thus, in a specific example of this type, the stilbene 70 is available from 1-bromo-2-nitrobenzene and α-iodocinnamaldehyde (Scheme 33).[181]
Meeeee 88 Meeee-Meeeeeee Meeeeeeee[888–888]
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8-(8-Meeeeeeeeeeee)-8,8-eeeeeeeeeeeeeeeeee-8-eeeeeeeeeeee (88):[888]
8-Meeeee-8,8-eeeeeeeeeeeeeeeeee-8-eeeeeeeeeeee (8.8 eeee, 8 eeeee), 8-eeeeeeeeeeeeeeeeeeee eeee (8.88 eeee, 8.8 eeeee), MMMM (8.88 eeee, 8 eeeee), Me(MMe)8 (8.888 eeee, 8 eee%), eee M8MM8 (8.88 eeee, 8.8 eeeee) eeee eeeee ee e eeeee-eeeeeeee eeeee (88 eM). Meeeeeeee M8M (8 eM) eee eeeee, eee eee eeeeeee eee eeeeeee eeeeeeeeee eee 8 e ee 88°M, eeeeeee eeee M8M (88 eM), eee eeeeeeeee eeee MeMMe (8 × 88 eM). Mee eeeeeee eeeee, eeee-eeeeeeee eeeeeeee, eee e eeeeee eeeee eeee eeeeeeeee eee eeeeeee eeeeeeee eeee eeeeeeee eee 88 eee, eeee eeeee (Me8MM8), eeeeeeee, eee eeee eeeeeeeeeeee. Mee eeeee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, MM8Me8); eeeee: 88%; ee 88°M.
References
[177] | Meeee, M.; Meeeee, M., Meeeeeeee, (8888), 888. |
[178] | Meeeeeeee, M.; Meeeeeeeeeeeee, M., Meee. Meee. Meee, (8888) 88, 888. |
[179] | Meeeee, M.; Meeeeeee, M.; Meeeeeeeeeeeee, M., Meee. Meee. Meee, (8888) 88, 888. |
[180] | Meeee, M.; Meeeeee, M. M., Mee. Meee., (8888) 8, 8888. |
[181] | Meeeeee, M. M.; Meeee, M. M.; Meeee, M. M.; Meeeee, M. M., Mee. Meee., (8888) 8, 8888. |
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- 8.Meeeee-Meee, (8888) 88/8e, 888.