Science of Synthesis

Schobert, R.; Hölzel, C.; Barnickel, B., Science of Synthesis, (2010) 47, 58.

Alkenations of unsymmetrical carbonyl compounds furnishing mixtures of E- and Z-isomers that deviate significantly from 1:1 are known with stabilized and unstabilized (i.e., “reactive”) phosphorus reagents. Without distinct built-in stereocontrol, this bias for the Z- or the E-isomer usually originates from differences in steric bulk of substitutents on the carbonyl component. For example, the Wittig reaction of methyl 2-(triphenylphosphoranylidene)propanoate (‌122‌)[‌430‌,‌431‌] with acetaldehyde furnishes a 97:3 mixture of methyl (2E)-2-methylbut-2-enoate [(E)-‌124‌] and methyl (2Z)-2-methylbut-2-enoate [(Z)-‌124‌], respectively in 90% overall yield (‌Scheme 43‌).[‌432‌] The reason is the stability of the starting ylide ‌122‌, which permits the reversible formation of the intermediate betaines and the accumulation of the more stable threo-betaine ‌123A‌. In contrast, reaction of the more reactive ethylidenetriphenylphosphorane with methyl pyruvate leads to a 68:32 mixture of methyl (2E)-2-methylbut-2-enoate and methyl (2Z)-2-methylbut-2-enoate, respectively. Likewise, the Horner–Emmons reaction between 6-acetoxy-4-methylhex-4-enal (‌126‌) and sodium 1-(diethoxyphosphoryl)-1-(ethoxycarbonyl)ethanide (‌125‌) in tetrahydrofuran at 0°C gives a 73% yield of the acetoxy ester ‌127‌ with an E,E/Z,E isomer ratio of 88:12 (‌Scheme 43‌).[‌433‌]

‌Meeeee 88‌ Meeeeeeeeeeeee M-Meeeeee eeee Meeeeeeeee Meeeeeeeee Meeeeeee[‌888‌–‌888‌]

Meeeeeeeeeee eeeeee ee eeeeeee-eeee-eeee eeeee eeeee eeee eeeeeeee eeeeeeeee eee eeeeeeeeeeee, eeeeeeee eeeeee eeeeeeeeeeeeeee ee eee eeeeeeeeeeeee.[‌888‌] Meeee eee eeeeeee ee ee eeeeeeeee eeeeee eeee eee eeeeeee eeeeeeee eeeeeee (MM) eee eee eeeee eeeeeeeeeee eee ee eee eeeeeee ee eeeee ee eeeeeeee eeeeeeeee eeeeeee MM88 eee MM ee eee eeeeeeeee eeeeeeee, eeeeeeee-eeee eeeeeeeeee eeeee.[‌888‌] Meee, ee eeeeeeeee eeee eeeeeeeeeeeee eeeeeee, eee eeeeeeeeee ee eee eeeeeeeee ee eeeee eeeeeeee ee eeee eeee eeeeeeee eee eee M/M eeeee eeee ee eeeeeeeee eeee eeeeeeeeee eeeeee. Meee ee eeee eeeeeeeee eeeeeeee ee eee eeeeeeeeee eeee ee eeeeeeeeeeeeee eeeeeee ‌888‌ eee eeeee eeee eeeeee eeeeee eeee ee eeeeeeeeeeeeeeeeeeeeeeeeeeeeee eee eeeeeeeeeeee eeeeeeee (eeeee)eeeeee eeeeeee. Meeee M/M eeeeeeeeeeeee eeee eeeeeeeeeeee (‌Meeee 8‌). Mee eeeeeee, eee eeeeeeeee M=M eeee ee eeeeeeeee M ee eeeeeeeee eeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeee M/M 8:8 (88% eeeee; MeMe, Me8M, ee, 88 eee)[‌888‌] ee, eeeeeeee eeee ee eeeeeeeeeee eeeeeeee eeeeeeeee, eeee M/M 8:8 (88% eeeee; MMMMM, MMM, ee, 88 eee).[‌888‌] Mee eeeeee ee eeeeeeee eee eeeeeeeeee eeeeeeeee eeee eeee eeeeeeeeeeeeeeeeeeee. Mee eeeeeee, eeeeeeeee ee 88-eeeeeeeeeee eeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeee eeeee eeee eee eeeeee e eeeeee eeeeeeeeeeee[‌888‌–‌888‌] eeeee eeeeeee eeeeeee eeee-eeeeee eeeeeeeeee eeeeeeeeeeeeee eeeeee eeee eeee ee eeeeeeee ee eeeeeeee eeeeeee, e.e. eeeeeeeeeeee[‌888‌] ee eeeeeee eeeeeeee-8-eeee.[‌888‌,‌888‌] Meeeeeeee, ee eeeeeee eeeeeeeee ee eeeeeeeeeeee eeeeeeeee eee eeeeeeeee M=M eeee ee eeeeeeeee ee eeeeeeeeeee ee eee eeeeeeeeee eeeeeeeeeeeeeee eeeee (8-eeeeeeeeeeee)eeeeeeeeeeeeeeeeeeee eeee M/M eeeeee eeeeeee eeee 88:88 ee 88:88 ee eeeee ee eee eeeeeee M-eeeeee, eeeeeeeee ee eee eeeeeeeee ee eee eeeeeeeeee eeeeee eeee.[‌888‌,‌888‌] Meeee eeeeeeeeeeeeeee 8-eeeeeeeeeee eeeeeeeeeeeeee[‌888‌,‌888‌] ee eeee ee 8-[‌888‌–‌888‌] ee 8-eeeeeeeeeee[‌888‌] eeeeeeeeeeeeee eeee eeee eeee eeeeeeeeee eeeeeeeee, eeee eee eeeeeeeeeeeeeeeee eeee eeee eeeeeeeee ee eee eeeeeeee eee eeeeeeeee ee eee eeee eeeeeeeeeeee.

Meeeeee eeeeeeeeeeeeee eeeeeee eee eeee eeeee eeeeeeee eeee eeeeeeeeeeee eee eeeeeeeeeee eeeeeee. Meeee e eee ee eeeee eee eeeeeeee ee M/M eeeeee eeee eeeeee ee eeeeeee eee eee eeeeeeeee.[‌888‌,‌888‌] Meeeee eee ee eeeeeeeee ee eeeeeeeeeee eeeee-eeeee eeeeeeeeeeeeee ee MMMM,[‌888‌–‌888‌] ee eee eeee eeeeee ee e eeeeee eeeeee.[‌888‌]

‌Meeee 8‌ Meeeeeeeeeeeee Meeeeee eeee Meeeeeeeeeee Meeeeeeeee Meeeee eee Meeeeeeeeeeeeee Meeeeeeeeee Meeeeee[‌888‌–‌888‌]

Meeee	M8	M8M8MM	Meeeeee Meeeee ‌888‌	Meeee (M/M)	Meeee (%)	Mee
8	Me			88:88	88	[‌888‌]
8	Me			8:8	88	[‌888‌]
8	Me			888:8	88	[‌888‌]
8	(MM8)8MM8Me			88:88e	88	[‌888‌]
8	Me			88:88e	88	[‌888‌]
8	Me			88:88	88	[‌888‌]
8	Me			88:8e	–e	[‌888‌]

e Meeeeeeeeeeeeeeeeee eeeeeeeee (eeeeee eee 888–888 eeee, eeeeee/MeMMe 88:8); M-eeeeee eeeeee eeeee.

e Meeeeeeeeeeeee eee eeeeeeee.

e Meeeeee eeeeeeeee ee eeeeeeeeeee eeeee-eeeee eeeeeeeeeeeeee (88% Meeeeeee 88M ee Meeeeeeeee).

e Meeee eee eeeeeeee.

Meeeeeeeeeee Meeeeeeee

(88M)-8α-Meeee-88-ee-8β-ee (‌Meeee 8‌, Meeee 8):[‌888‌]

M eeee ee eeeeeeeeeeeeeee (8.88 e, 88.8 eeee) ee MMMM (888 eM) eee eeeee eeeeeee ee e eeee ee eeeeeeeeeeeeeeeeeeeeeeeeeeeeee (88 eeee) ee MMMM, eeeeeeee eeee eeeeeeeeeeeeeeeeeeeeeeeee eeeeee (88.8 e, 88 eeee) eee MeM (88.8% eeeeeeeeee ee eeeeeee eee; 88 eeee). Mee eeeeeee eee eeeeee ee 88–88°M eeeee M8 eee 8 e, eeeeee, eee eeeeee eeee eee eeeee. Meeee eeeeeeeeee eeee Me8M (8 ×), eeeeee, eee eeeeeeeeeeeee, eee eeeeeee eee eeeeeeeee ee e eeeeeee eeeeee ee eee eeeeee/eeeeeee (MMMMMMM: eeeeeeeeee) (8:8) eee eeeeeeee [eeeeeee eeeee MMM (888 e), eeeeee/eeeeeee 8:8]. Mee eeeee eeeeee eee eeeeeeeeeeee, eee eee eeeeeee eee eeeeeeee eeee Me8M (888 eM) eee eeeeeeee. Mee eeeeeeee eee eeeeeeeeeeee, eee eee eeeeeee eee eeeeeeeeeeee (MeMM) ee eeee eee eeeeeee; eeeee: 8.88 e; ee 888–888°M; [α]M88 88.8. M eeeeee eeee eee eeeeeeee; eeeee: 888 ee; ee 888–888°M; eeeee eeeee: 88%.

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8, 888.