Science of Synthesis

Petasis, N. A., Science of Synthesis, (2010) 47, 232.

Several types of gem-dimetallic reagents, which are generated in situ from gem-dihalides and activated metals, are able to perform the alkylidenation of carbonyl compounds, often with high control of geometry (‌Table 29‌).[‌147‌,‌148‌,‌152‌,‌155‌,‌220‌–‌226‌] Aldehydes are converted into alkenes (‌Table 29‌, entry 1),[‌220‌] alkenylsilanes (entry 2),[‌221‌] alkenyl sulfides (entry 3),[‌221‌] and alkenylstannanes (entry 4)[‌222‌] with predominantly E-geometry using gem-dihalides and chromium(II) chloride. A samarium-based system has been reported that converts ketones into tri- and tetrasubstituted alkenes (entry 5),[‌223‌] while a process using titanium(II) chloride mediated by activated zinc converts aldehydes and ketones into alkenylsilanes (entry 6).[‌155‌] The Takai–Utimoto protocol for methylenation (see Section ‌47.1.1.4.4‌) can be adapted for the alkylidenation of carboxylic acid derivatives by using higher homologues of gem-dihalides. This method works well with a variety of carbonyl compounds including esters,[‌147‌,‌148‌,‌152‌,‌206‌,‌224‌] silyl esters,[‌225‌] thioesters,[‌224‌,‌226‌] lactones,[‌152‌] and amides,[‌226‌] forming the corresponding alkene products often with good Z/E selectivity (entries 7–14).[‌147‌,‌148‌,‌152‌,‌224‌–‌226‌] As with the methylenation variant of this process, the formation of the reactive gem-dimetallic species is catalyzed by lead(II) chloride, while the use of N,N,N′,N′-tetramethylethylenediamine presumably enables the formation of a titanium carbene, which can also perform ring-closing metathesis leading to cyclic and heterocyclic products.[‌227‌] Intramolecular alkylidenations based on this process are also possible.[‌228‌]A number of other gem-dimetallic alkylidene systems, including Tebbe-like derivatives,[‌229‌] that involve zirconium/aluminum,[‌229‌,‌230‌] zinc/magnesium,[‌231‌] magnesium/magnesium,[‌232‌] or zinc/zirconium[‌230‌] species are also able to perform alkylidenations of carbonyl compounds.

‌Meeee 88‌ Meeeeeeeeeeeee eeee eee-Meeeeeeeee Meeeeeee[‌888‌,‌888‌,‌888‌,‌888‌,‌888‌–‌888‌]

Meeee	Meeeeeee Meeeeeee	Meeeeeeeee	Meeeeee	Meeee (M/M)	Meeee (%)	Mee
8		MeMMM8, MeMe8, MMM, 88°M		888:8	88	[‌888‌]
8		MMMMMMe8, MeMe8, MMM, 88°M		888:8	88	[‌888‌]
8		MeMMMMe8, MeMe8, MMM, 88°M		88:88	88	[‌888‌]
8		Me8MeMMM8, MeMe8, MMM, 88°M		–	88	[‌888‌]
8		Me8MMMe8, Me, MeM8, MeMe8 (eee.), MMM, 88°M		–	88	[‌888‌]
8		MMMMMMe8, Me, MeMe8 (eee.), MeMe8, MMM, 8–88°M		88:88	88	[‌888‌]
8		MeMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, MM8Me8, 88°M		8:88	88	[‌888‌,‌888‌,‌888‌]
8		MMMMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, MM8Me8, 88°M, 8 e		88:88	88	[‌888‌]
8		MeMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, 88°M, 8 e		8:88	88	[‌888‌]
88		MeMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, 88°M, 8.8 e		8:888	88	[‌888‌]
88		MMMMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, MM8Me8, 88°M, 8 e		8:88	88	[‌888‌]
88		MeMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, 88°M		88:88	88	[‌888‌]
88		Me(MM8)8MMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, 88°M		8:88	88	[‌888‌]
88		MeMMMe8, Me, MeMe8 (eee.), MeMe8, MMMMM, MMM, 88°M		88:8	88	[‌888‌]

Meeeeeeeeeee Meeeeeeeee

(M)-8-Meeeee-8-(eeeeeeeeeeeeee)eeeeee (‌Meeee 88‌, Meeee 8); Meeeeee Meeeeeeee:[‌888‌]

M eeee ee MeMMM (8.88 e, 8.8 eeee) eee MMMMMMe8 (8.88 e, 8.8 eeee) ee MMM (8 eM) eeeee ee eeeee eeeeeeeeee eee eeeee ee 88°M ee e eeeeeee eeeeeeeeee ee MeMe8 (8.88 e, 8.8 eeee) ee MMM (88 eM). Mee eeeeeeeee eeeeeee eee eeeeeee ee 88°M eee 88 e (eee eeeee eeeeeee eeeeeeeee eeee eeee ee eeeeeeee eeeeee) eee eeeeee eeee M8M (88 eM), eee eee eeeeeeeee eeeeeee eee eeeeeeeee eeee eeeeee (8 × 88 eM). Mee eeeeeeee eeeeeeee eeee eeeee (Me8MM8) eee eeeeeeeeeeee. Meeeeeeeeeee ee eee eeeee eeeeeee ee eeeee eeeeee eeeeeeeeeeeeee (eeeeee eee, eeeeee) eeee eee eeeeeee ee eee M-eeeeee; eeeee: 8.88 e (88%).

[(M)-8-Meeeeeeee-8-eeee]eeeeeee (‌Meeee 88‌, Meeee 8); Meeeeee Meeeeeeee:[‌888‌,‌888‌,‌888‌]

M 8.8 M eeee ee MeMe8 (8.8 eeee) ee MM8Me8 eee eeeee ee 8°M ee MMM (88 eM) eeeee ee eeeee eeeeeeeeee. MMMMM (8.8 eM, 8.8 eeee) eee eeeee ee eee eeeeee eeee ee 88°M, eee eee eeeeeee eee eeeeeee ee 88°M eee 88 eee. Me eeee (8.88 e, 8.8 eeee) eee eeeee, eeeeeeee ee MeMe8 (8.88 e, 8.888 e, 8.888 eeee), eee eee eeeeeee eee eeeeeee eee 88 eee ee 88°M (eee eeeee ee eee eeeeeeeeee eeeeeee eeee eeeeeeee eeeeee ee eeee eeeeeeee eeee ee e eeeeeeee eeeeeeeeee eeeeeee). M eeee ee MeMMe (8.888 e, 8.8 eeee) eee MeMMMe8 (8.88 e, 8.8 eeee) ee MMM (8 eM) eee eeeee, eee eee eeeeeee eee eeeeeee ee 88°M eee 8 e (eee eeeee ee eee eeeeeeeee eeeeeee eeeeeeeee eeeeee eeee eeeee). Mee. M8MM8 eeee (8.8 eM) eee eeeee ee 8°M, eee eee eeeeeee eee eeeeeee ee 8°M eee e eeeeeee 88 eee, eeeeeee eeee Me8M (88 eM), eee eeeeee eeeeeee eeeeeee e eeeee eeeeee [eeeee eeeeeee (eeeeeeee MMM), Me8M/Me8M 888:8 (888 eM)]. Mee eeeeeeeee eeeee eeee eee eeeeeeeeeeee, eee eee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee [eeeee eeeeeee (eeeeeeee MMM), eeeeeee] ee eeee eee eeeeeee ee e 8:88 eeeeeee ee M- eee M-eeeeeee; eeeee: 8.88 e (88%).

References