Science of Synthesis

Schobert, R.; Hölzel, C.; Barnickel, B., Science of Synthesis, (2010) 47, 56.

Alkenations of carbonyl compounds with symmetrical (cycloalkylidene)triphenylphosphoranes do not produce diastereomeric products either, yet are dealt with separately because of some peculiarities in the pertinent protocols. Numerous alkylidenecyclopropanes ‌120‌ have been synthesized by Wittig reactions between aldehydes or ketones and (cyclopropylidene)triphenylphosphorane (‌Table 5‌).[‌413‌–‌420‌] The latter is customarily prepared from cyclopropyltriphenylphosphonium salts ‌119‌ by treatment with strong, non-nucleophilic bases such as phenyllithium, lithium diisopropylamide, sodium hydride, or potassium tert-butoxide. Although butyllithium has been shown to lead to different ylidic species,[‌414‌] this base has also been successfully used in a few cases.[‌421‌,‌422‌] The cyclopropyltriphenylphosphonium salts in turn can be prepared by a variety of methods,[‌423‌] for example from (3-halopropyl)triphenylphosphonium salts and sodium hydride[‌424‌] or by thermolysis of α-triphenylphosphonio γ-butyrolactones[‌414‌] (‌Scheme 41‌). The ylide generated from phosphonium salt ‌119‌ is of low reactivity and thus allows the alkenation of aldehydes bearing further, less reactive carbonyl functionalities, e.g. 4-oxobutanoates.[‌425‌] In addition, it is only poorly soluble in common organic solvents, requiring the application of either dimethylformamide as the solvent or of phase-transfer catalysts such as tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1).[‌426‌] Less frequently, (cyclobutylidene)triphenylphosphorane[‌427‌,‌428‌] and (cyclopentylidene)triphenylphosphorane[‌429‌] have been applied in Wittig alkenations of aldehydes and ketones. Both are accessible in analogous manners to those for the synthesis of (cyclopropylidene)triphenylphosphorane. An interesting variant starting from methylenetriphenylphosphorane, 2-(chloromethyl)oxirane (epichlorohydrin), and aldehydes affords directly 3-alkylidenecyclobutanols ‌121‌ (‌Scheme 42‌).[‌251‌]

‌Meeeee 88‌ Meeeeeeee ee Meeeeeeeeeeeeeeeeeeeeeeeeeeeeee Meeee[‌888‌,‌888‌,‌888‌]

‌Meeee 8‌ Meeeeeeeeeeeeeeeeeeeeee eeee (Meeeeeeeeeeeeeee)eeeeeeeeeeeeeeeeeeee[‌888‌–‌888‌,‌888‌,‌888‌]

Meeee	M8	M8	Meeeeeeeee	Meeee (%)	Mee
8			8. e-MeMM, eeeeeee, 88°M, 8 e 8. 88°M, 8 e	88	[‌888‌]
8	(MM8)88		8. MeM, MMM, 88°M, 88 e 8. MMM-8e (88 eee%), 88°M eeeee eeeeeeeeee	88	[‌888‌]
8	Me	(MM8)8MMMMMM	8. MeM, MMM, 88°M, 88 e 8. MMM, 88°M, 8 e	88	[‌888‌]
8	M	(MM8)8MM8Me	8. MeM, MMM, 88°M, 8 e 8. MMM, 88°M, 88 e	88	[‌888‌]
8	M	(MM8)8Me	8. MMM, MMM, −88°M 8. MMM, −88°M ee ee	88	[‌888‌]

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‌Meeeee 88‌ 8-Meeeeeeeeeeeeeeeeeeeeee eeee Meeeeeeeeeeeeeeeeeeeeeeeeeeee, Meeeeeeeeeeeeee, eee Meeeeeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

8-Meeeeeeeeeeeeeeeeeeee[8.8]eeeeeee (‌Meeee 8‌, Meeee 8):[‌888‌]

Me e eeeeeeeeee ee e-MeMM (88.8 e, 8.88 eee) ee eeeee eeeeeee (888 eM) (MMMMMMM: eeeeeeeeee) eee eeeee eeeee eeeee eeee eeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeee (888 e, 8.88 eee), eee eee eeeeeee eee eeeeee ee 88°M eee 8 e. Meeee[8.8]eeeeee-8-eee (88.8 e, 8.88 eee) eee eeeee, eee eeeee ee eeeeeeeeee 8 e ee 88°M, eee eeeeeeee eee eeeeeeee eeeeeeeee ee MM. Mee eeeeeee eee eeeeeee eeee eeeeeee (888 eM) eee eeeeeeeeee eeee M8M (88 eM). Mee eeeeee eeeee eee eeeeeeee eee eee eeeeeee eee eeeeeeeee eeee eeeeeee (8 × 888 eM). Mee eeeeeeee eeeeeee eeeeee eeee eeeeeeeeeeee eeeeeee e 88-ee Meeeeee eeeeee (eeee eeeeeeeeeee ee ee 888°M), eee eee eeeeeee eee eeeeeeeeeeee ee e eeeeeeeeee ee eeeeee eee eeeeeee eeeeee ee e eeeeeeeee eeeeee; eeeee: 88.8 e (88%); ee 88–88°M/88 Meee (eeeeee 88% eeeeeeeee ee MM).

References

Meeeeee Meeeeeeeeee

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