Science of Synthesis

Schobert, R.; Hölzel, C.; Barnickel, B., Science of Synthesis, (2010) 47, 62.

The synthesis[‌371‌] of dibenzophosphole-based ylides such as ‌131‌ and their application in consistently E-selective alkenations of aldehydes[‌371‌] and ketones with sufficiently different branching at the α- and α′-carbons has been reported.[‌470‌] Such ketones give rise to trisubstituted alkenes ‌132‌ with E/Z ratios of up to 98:2 (‌Scheme 45‌). Salt-free dibenzophosphole ethylide ‌131‌ can be generated in tetrahydrofuran by deprotonation of the phosphonium salt, which is available from commercial tetraphenylphosphonium bromide, with potassium hexamethyldisilazanide, as shown in ‌Scheme 45‌.[‌371‌] The cooled ylide solution is then treated with the ketone, warmed to room temperature, and finally heated under nitrogen at 100°C for some time in order to cleave the oxaphosphetane intermediate and to induce alkene formation. A second drawback, aside from the necessity to heat the reaction mixture, is the fact that only one of the two identical P-alkyl substituents in the precursor phosphonium salt is utilized in the Wittig reaction. Bridged tetrahydrophosphole ylides such as ‌133‌ circumvent these problems.[‌372‌] They are available from a known bicyclic phosphine.[‌471‌]

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‌Meeeeeeeeee 88‌

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‌888‌	Me	Me	8:88	88	[‌888‌]
‌888‌	Me	Me	8:88	88	[‌888‌]
‌888‌		Me	88:88	88	[‌888‌]
‌888‌		Me	8:88	88	[‌888‌]
‌888‌	(MM8)8MMMe		88:88	88	[‌888‌]
‌888‌	(MM8)8MMMe		8:88	88	[‌888‌]
‌888‌	MM8MMMM	Me	88:88	88	[‌888‌]
‌888‌	MM8MMMM	Me	88:88	88	[‌888‌]

Meeeeeeeeeee Meeeeeeee

(M)-8-(Meeeeeee-8-eeee)eee-8-eee [‌888‌, M8 = Meeeeeee-8-eeee; M8 = Me]; Meeeeee Meeeeeeee:[‌888‌]

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