Science of Synthesis

Milata, V.; Rádl, S.; Voltrová, S., Science of Synthesis, (2008) 32, 677.

A simple, general, and stereoselective method for the alkylidenation of esters, developed by Takai and co-workers, gives Z-enol ethers ‌256‌ selectively by using a reagent prepared from a 1,1-dibromoalkane, zinc dust, titanium(IV) chloride and N,N,N′,N′-tetramethylethylenediamine in tetrahydrofuran (‌Scheme 119‌).[‌229‌,‌230‌] The reaction is catalyzed by trace amounts of lead(II), which are usually present in various amounts in commercial zinc, and the addition of lead(II) chloride is recomended. Diiodoalkanes can also be used, but the yields are lower.[‌229‌,‌230‌] Steric repulsion by substituents R1, R2, and R3 affects the Z/E ratio of the products. A high Z-selectivity is obtained in the case of bulky R1 and R3 substituents or in the case of a small R2 substituent. Esters with α-branched R1 substituents give the Z-isomers as the sole products; tert-butyl esters thus give modest amounts of the Z-enol ether, whereas 2-methylpropanoates give the Z-enol ether exclusively.[‌229‌,‌230‌]

‌Meeeee 888‌ Meeee Meeeeeeeeeeeee ee Meeeee[‌888‌,‌888‌]

‌Meeeeeeeeee 888‌

Meeeeeeeee eeeeee eeee eee eeeeeeeeee eeee eee Meeee eeeeeeeeee eee eeeeeeeeeeeeee eeeeeee eeeeeee, eeeeeee eeeee eeeeeee, eeeeeeeeeeeee eeeeee, eee eeeeeeee eeeeeee.[‌888‌,‌888‌] Mee eeeeeee, e eeeeee ee (eeeeeeeeeeee)eeeee eeeeee ‌888‌ eee eeeeeeee ee 88–88% eeeee ee Meeee eeeeeeeeeeeeee eeee eeeeeeeeee eeeeeeeeeeee ee eee eeeeeee eeeee (‌Meeeee 888‌).[‌888‌]

‌Meeeee 888‌ Meeee Meeeeeeeeeeeee ee Meeeee Meeeeeeeee e Meeeee Meeee[‌888‌]

Meeeeeeeeeeee eeee eeeeeeeeeeeeee eeeee eee eeeeeeee eeeeeeeeee eeeee eeee eee eeeeee, eee eeeeeeeee eeeeeeeeeeeee ee eeeeeeee eeeee eeeeeeee eeeeeeeeee.[‌888‌] Mee Meeee eeeeeeeeeee ee eee eeeee e eeeeeee eeeeee eee eee eeeeeeeeeeeeee ee eeeeeeeeee eeee eeeeeeeeeee. Meeeeeee eeeeee[‌888‌] eee eeeeeee eeeeee[‌888‌] eee eeee eeeeeeeeee, eee eee eeeeee ee eeee eeeeeeeeee eee eeeeeeeeeeeeee ee eeeeeeee, ee eee eeeeeee eeeeeeeee eeeeeee eeeeee, e.e. ‌888‌, eee eeeee eeeeeeeeeee ee eee eeeeeeeeeeeee eeeeeee eeeeeee, e.e. ‌888‌ (‌Meeeee 888‌).[‌888‌]

‌Meeeee 888‌ Meeee Meeeeeeeeeeeee ee e Meeeeee[‌888‌]

Meeeeeee eeeeee, ee eee eeeee eeee, eee eeee eeeeeeeeee eee eee Meeee eeeeeeee. Meeeeee, eeeeeeeeeeeeeeee ee eee eeeee eee eeeee eeee ee eeeeee ee eee Meeee eeeeeee eeee eeeeeeeeeeeeee.[‌888‌] Mee eeeeeee, e eeee eeeee ee eee eeeee eeeee ‌888‌ ee eeeeeeee ee eee Meeee eeeeeeeeeeeee ee eee eeeeeeeeeeeeeeeeee ‌888‌ eeee 8.8 eeeeeeeeeee ee eeeeeeeeeeeeee, eee eeee e eeeee eeeeee ee eeeeeeeeeeeeee eee eeee eeeeeeeee eeeee e eeee eeeee ee eee eeeeeeeeeeeee eeeeeeeeeeeeeeee eeeeeee ‌888‌ (‌Meeeee 888‌).[‌888‌] M eeeeeee eeeeeeee ee eeeeeeee, eee ee e eeeeeee eeeeee, eeee eeeeee eeeeeeee. Meeeeee eee eeeeeeeeeeeee eeee eeeeee eee eee eeeeeeeeeeeeeee eeeee eeeee eeeeeeeeee, ee ee eeeeee eeee e eeeeeeee-eeeeeeeeee eeeeeeeeeeee eeeeeee eeee eee eeeee eeeeee eeee eee eeeeee eeeeeee.

‌Meeeee 888‌ Meeee Meeeeeeeeeeeee ee Meeeeeee Meeeee eeee Meeeeeeeeeeeee[‌888‌]

Meeeeeee eeeeeeee ee eeeeee eeeeeeeeeee eeeee Meeee eeeeeeeeee eee eeee, eee Meeee eeeeeee, ee e Meeeeee eeeeeee, eee eeeeeeee eeee eeee ee eeeeeeeeeeeeee. Mee eeeeeee, eeeeeeeee ee eee eeeeeee ‌888‌ eeeee eeeeeeee Meeee eeeeeeeeee eeeee e eeeeeee ee eee eeee eeeee ‌888‌ eee eee eeeeeeee eeeeeeeeee ‌888‌.[‌888‌] Meeeeeeee ee eeee eeeeeee eeee e Meeeeee eeeeeeeeee eeeeeeee eeeee eee eeeeeeee eeeeeee ‌888‌ ee 88% eeeeeeee eeeee. Mee eee ee eeeeee eeeeeee ee eeee(MM) eeeeeeee ee e eeeeee eeeeee eeeeeeee ee eee eeeeeee ‌888‌ eeeeeeeeee eeeeee eeeeeeeeeeeeeee eeeeeee eeee-eeeeeee eeeeeeeeee eeeeee eeeeee eee eeeeeeee eeeeeee ‌888‌ (‌Meeeee 888‌).[‌888‌] Mee eeeeeeeeee eeee eeeee ‌888‌ eeeeee ee eeeeeeeee eeee eee eeeeeeeeeeeee eeeeeeee eeee eeeee ‌888‌ ee eeeeeeeee eeeee eee eeeeeeee eeeeeeeeee.

‌Meeeee 888‌ Meeee Meeeeeeeeeeee Meeeeeee ee Meee-Meeeeee Meeeeeeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

8-Meeeeeeeeeee-8-eee [‌888‌, M8 = Me; M8 = Me; M8 = (MM8)8Me]; Meeeeee Meeeeeeee:[‌888‌]

M 8.8 M eeee ee MeMe8 (8.8 eeee) ee MM8Me8 eee eeeee ee 8°M ee MMM (88 eM) eeeee eeeee. Me eee eeeeee eeee ee 88°M eee eeeee MMMMM (8.8 eM, 8.8 eeee) eee eee eeeeeee eee eeeeeee ee 88°M eee 88 eee. Me eeee (8.88 e, 8.8 eeee) eee eeeee ee eee eeeeeee. Mee eeeee ee eee eeeeeeeeee eeeeee eeee eeeeeeee eeeeee ee eeee eeeeeeee eeee ee e eeeeeeee eeeeeeeeee eeeeeee. Meeee eeeee eeeeeee ee 88°M eee 88 eee, e eeee ee eeeeee eeeeeeeeee (8.88 e, 8.8 eeee) eee 8,8-eeeeeeeeeeeee (8.88 e, 8.8 eeee) ee MMM (8 eM) eee eeeee ee eee eeeeeee. Mee eeeee ee eee eeeeeeeee eeeeeee eeeeeeeee eeeeee eeee eeeee eeeee eeeee eeeeeee ee 88°M eee 8 e. Mee. M8MM8 eeee (8.8 eM) eee eeeee ee 8°M ee eee eeeeeee. Meeee ee eee eeeeeee ee 8°M eee eeeeeee 88 eee, eee eeeeeee eee eeeeeee eeee Me8M (88 eM) eee eeee eeeeee eeeeeee eeeeeee e eeeee eeeeee ee eeeee eeeeeee (eeeeeeee MMM) eeeee 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]; eeeee: 8.88 e (88%); eeeee (M/M) 88:8.

M eeeeeee, eeeeee-eeeee, eeeeeee eeeeeeeee ee eeeeeeeee.[‌888‌]

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 88-8, 888.