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47.1.1.4.1.1 Variation 1: Methylenation of Aldehydes

DOI: 10.1055/sos-SD-047-00100

Petasis, N. A.Science of Synthesis, (201047166.

The methylenation of aldehydes with the Tebbe reagent 12 often proceeds with modest yields due to subsequent reaction of the monosubstituted alkene product to form titanacyclobutanes (see Scheme 2). However, this process can be more efficient for more hindered aldehydes, which, given the nonbasic nature of the Tebbe reagent, also proceeds without any epimerization (Table 1).[‌27‌‌29‌] For example, (2S,3R)-3-(tert-butyldimethylsiloxy)-2-methylpentanal (Table 1, entry 1)[‌27‌] is methylenated in only 46% yield, while the more complex aldehyde (3S,4S,5R,6S,8R)-5-[(benzyloxy)methyl]-8-(tert-butyldimethylsiloxy)-6-hydroxy-5-methyl-1-oxaspiro[2.5]octane-4-carbaldehyde (entry 2)[‌28‌] (used as a lactol mixture), and the bulkier aldehyde (7S)-3,7-anhydro-4,6-dideoxy-6-methyl-7-[(1E)-prop-1-enyl]-2,5-bis-O-(tert-butyldimethylsilyl)-D-talo-heptose (entry 3)[‌29‌] are converted into the corresponding alkenes in higher yields (76 and 95%, respectively).

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Meeee Meeeeeee Meeeeeee Meeeeeeeee Meeeeee Meeee (%) Mee
8 Meeee eeeeeee 88, eeeeeee, MMM, 8°M 88 [‌88‌]
8 Meeee eeeeeee 88, eeeeeee, MMM, 8°M 88 [‌88‌]
8 Meeee eeeeeee 88, eeeeeee, MMM, 8°M 88 [‌88‌]

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Meeee 8 Meeeeeeeeeeee ee Meeeeeeee ee eee Meeeeeee ee Meeeeeeeee Meeeeeee Meeeee[‌88‌‌88‌]

Meeee Meeeeeee Meeeeeee Meeeeeeeee Meeeeee Meeee (%) Mee
8 Meeee eeeeeee 88, eeeeeee, MMM, 8°M 88 [‌88‌]
8 Meeee eeeeeee 88, eeeeeee, MMM, 88°M 88 [‌88‌]
8 Meeee eeeeeee 88, eeeeeee, MMM, 8°M 88 [‌88‌]
8 Meeee eeeeeee 88, eeeeeee, MMM, eeeeeeee, 88°M 88 [‌88‌]
8 Meeee eeeeeee 88, eeeeeee, MMM, eeeeeeee, 88°M 88 [‌88‌]

Meeeeeeeeeee Meeeeeeee

(8M,8M)-8,8-Meeeeee-8,8-eeeeeee-8-eeeeee-8-[(8M)-eeee-8-eeee]-8-M-(eeee-eeeeeeeeeeeeeeeeee)-8-[(8M)-8-(eeee-eeeeeeeeeeeeeeeeeee)eeee-8-eeee]-M-eeeee-eeeeeeee (Meeee 8, Meeee 8); Meeeeee Meeeeeeee:[‌88‌]

Me e eeee ee eee eeeeeeee (888ee, 8.88eeee) ee MMM (88eM) ee 8°M eee eeeee e 8.8M eeee ee eee Meeee eeeeeee 88 ee eeeeeee (8.8eM, 8.88eeee). Meeee 88eee ee eeee eeeeeeeeeee, eee eeee eee eeeeeee eeee Me8M (88eM), eee eee eeeeeeee eee eeeeeeee ee eee eeee eeeeeeee ee 8M MeMM (8.8eM). Mee eeeeeeeee eeeeeee eee eeeee (MeMM8), eee eee eeee eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee. Meeee eeeeeeeeeeeeee eeeeeeee e eeeeeeeee eee; eeeee: 888ee (88%).

(8M,8M,8M,8M)-8,8,8,8-Meeeeeee(eeeeeeeee)eeee-8,8-eeeee (Meeee 8, Meeee 8); Meeeeee Meeeeeeee:[‌88‌]

M eeeeeeeeeeee eeeeeeee 8.8M eeee ee eee Meeee eeeeeee 88 ee eeeeeee (8.8eM, 8.8eeee) eee eeeeeee eeee MMM (8eM), eee eee eeeeeeeee eeee eee eeeee eeeeeeee eeee 8e ee e eeeeee (88°M) eeee ee eee eeeeeeeeee (888ee, 8.888eeee) eee eeeeeeee (8.8eM) ee MMM (88eM). Mee eeeeeee eee eeeeee eeeeee ee eeeeeee eeeeeeeeeee eee eeeeeee eee 88eee. Mee eeeeeeee eee eeeeeeee ee eeeeeeee ee e eee eeeee ee 8M ee MeMM ee 88°M, eee eeeeeee eee eeeeeee eee 88eee, eeeeeeeee eeeeeeee eeee eeeeeee ee eeeeeeeeee eeeeeee e eee ee Meeeee, eee eee eeeeeeee eee eeeeeeeeeeee. Meeee eeeeee eeeeeeeeeeeeee (eeeeee/MeMMe 88:8) ee eee eeeeeee eeeeeeee e eeeeeeeee eeeee; eeeee: 88.8ee (88%).

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