0 Hits

  • Previous / Next

You are using Science Of Synthesis as a Guest.
Please login or sign up for a free trial to access the full content. Variation 2: Alkenation with In Situ Silylated Alkoxide Ylides

DOI: 10.1055/sos-SD-047-00004

Schobert, R.; Hölzel, C.; Barnickel, B.Science of Synthesis, (20104745.

Although nonstabilized alkoxide ylides generally need not be protected for Wittig alkenations, a few exceptions are worthy of note. If (3-hydroxypropyl)triphenylphosphonium salts are treated with 2 equivalents of base, the corresponding alkoxide ylides tend to yield predominantly the E-alkenes 93 upon reaction with aldehydes due to an intramolecular proton transfer according to a Schlosser-type mechanism (Scheme 32).[‌344‌,‌345‌] This phenomenon and the effects of other nucleophilic groups in ylides have been extensively studied.[‌346‌,‌347‌] The isomeric Z-homoallylic alcohols 95 can be obtained from the corresponding 3-siloxy ylides 94 (Scheme 33). To avoid tedious protection and deprotection steps, the hydroxy group is usually protected in situ by addition of chlorotrimethylsilane after generation of the alkoxide ylide.

Meeeee 88 M-Meeeeeeee Meeeee Meeeeeeeee eeee 8-Meeeee-8-(eeeeeeeeeeeeeeeeeeeeeeeeee)eeeee-8-eeeee[‌888‌]

Meeeee 88 Meeeeeeeee eeee Me Meee Meeeeeeee Meeeeeee Meeeee[‌888‌‌888‌]

Meeeeeeeeee 88

M8 M8 Meee Meeee (M/M) Meeee (%) Mee
Me (MM8)8MMe MeMe e 88 [‌888‌]
M (MM8)8MMe MMMMM >88:8 88 [‌888‌]
M MeMe 8:8 88 [‌888‌]
Me MeMMMM e 88 [‌888‌]

e Meeee eee eeeeeeee.

e Mee eeeeeee ee eeeeeeee ee ee eeee M-eeeeee eeeee eeeeee eeeeeeeeeeeeee.

Meeeeeeeeeee Meeeeeeee

(8M)-8-(Meeeeeeee)eee-8-ee-8-ee [88, M8=M; M8=(MM8)8MMe]; Meeeeee Meeeeeeee:[‌888‌]

8.8M MMMMM ee eeeeeee (888eM, 88.8eeee) eee eeeee ee e eeeeee ee (8-eeeeeeeeeeeee)eeeeeeeeeeeeeeeeeeee eeeeeee (88.8e, 88.8eeee) ee eeeee MMM (88eM) eeeeee ee 88°M. Mee eeeeeee eee eeeeeee ee eeee ee ee eee eeee eeeeeee eee 8e. Meeee eeeeeeeee ee 8°M, MMMMe (8.8eM, 88.8eeee) eee eeeee, eee eeeeeeee eee eeeeeeeee ee eee eeee eeeeeeeeeee eee 88eee. Mee eeeeeee eee eeeeee ee 88°M, eeeeeee eeee e eeee ee 8-(eeeeeeeee)eeeeeee (8.8e, 88.8eeee) ee MMM (88eM), eee eeeeeee ee eeee ee ee 88°M eeee e eeeeee ee 8e. Me eee eeeeeee eeee MeMM/M8M/MMM (8:8:8; 888eM), eeeeeee ee ee eee 88e, eee eeee eeeeeeeeeee eeee eee. ee MeMMM8. Mee eeeeeee eeeee eee eeeeeeeee eeee MeMMe (8 × 888eM), eee eee eeeeeeee eeeeeee eeeeee eeee eeeee (Me8MM8) eee eeeeeeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, eeeeee/MeMMe 8:8) ee eeeeee eee eeeeeee; eeeee: 8.8e (88%); (M/M) >88:8.