Science of Synthesis

Negishi, E.; Wang, G., Science of Synthesis, (2009) 46, 246.

Treatment of E-alkenylboranes with alkynyllithium reagents, followed by successive addition of iodine and then sodium hydroxide, produces 1,4-disubstituted conjugated E-enynes that can be readily converted into 1,4-disubstituted E,Z-1,3-dienes[‌2‌,‌10‌] (‌Scheme 10‌; see also Section ‌46.10.1.2.1‌). Even today, it is one of the most efficient, selective, and widely applicable methods for the synthesis of 1,4-disubstituted E,Z-1,3-dienes, although its application is still rather limited. The enyne-formation process via iodine-induced migratory insertion has been applied to the synthesis of (Z)-1-halo-1-en-3-ynes.[‌11‌] The scope of this method has been further expanded through the use of other electrophiles, such as the boron trifluoride–diethyl ether complex.[‌12‌] A series of methods for the preparation of Z-alkenylboranes has become available since 1975,[‌13‌–‌15‌] and they can, in principle, be used in place of the E-1,3-enynes to prepare Z,Z-1,3-dienes. As the diene-forming step is formally a reduction, it is not discussed further here. Synthesis of the insect pheromones bombykol[‌2‌] and that of a European grapevine moth, Lobesia botrana,[‌10‌] demonstrate the high efficiency and selectivity of this method. All isolated products are ≥98–99% stereomerically pure.

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References

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• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) 88/8e, 888.
• 8.Meeeee-Meee, (8888) 88/8e, 888.