Science of Synthesis

Hirsch, A.; Vostrowsky, O., Science of Synthesis, (2008) 43, 77.

The rearrangement of a carbene or a carbenoid intermediate to form an acetylene, known as the Fritsch–Buttenberg–Wiechell rearrangement (see also Sections ‌43.8.1.2.2‌ and ‌43.8.2.1.5‌),[‌268‌–‌270‌] is highly suitable for the formation of polyynes and polyyne frameworks within highly conjugated organic materials.[‌271‌] Thus, treating a 2,2-disubstituted 1,1-dibromoethene with butyllithium under mild conditions generates a carbene or carbenoid, which subsequently rearranges by a 1,2-migration of one of its substituents into a 1,2-disubstituted alkyne. Mixed rearrangements, in which one of the migrating groups is an alkyne and the other a vinyl, aryl, or hetaryl group, offer a convenient synthesis route to conjugated alka-1,3-diynes ‌123‌ (‌Table 8‌). Here, the dibromoethene–carbene precursors ‌122‌ are best prepared through the initial formation of an alkynyl ketone, followed by dibromoalkenation under Corey–Fuchs conditions.[‌272‌] The corresponding ketones can be obtained by three different routes, namely Grignard type reactions, Friedel–Crafts acylations, and Corey–Fuchs–Wittig alkenations.[‌272‌] The success of the Fritsch–Buttenberg–Wiechell rearrangement depends on the choice of solvent, and apolar hydrocarbon solvents such as hexanes, toluene, or benzene work quite well. The Fritsch–Buttenberg–Wiechell rearrangement can be applied to the formation of silyl-, alkyl-, alkenyl-, and arylated polyynes, including di-, tri-, and tetrayne products, as well as the construction of two-dimensional carbon-rich molecules.[‌271‌] A series of dibromoalkenes are converted into alka-1,3-diynes by treatment with butyllithium in dry hexanes at low temperature, and typically such reactions are over by the time the mixture has been allowed to warm to −40°C (‌Table 8‌, entries 1–11).[‌273‌,‌274‌] Among the rearrangement products (entry 11) is the diene–diyne atractylodin that may be isolated from medicinal plants of the Atractylodes genus.[‌274‌] When 4,4-dibromo-3-phenylbut-3-en-1-yne is treated with butyllithium (2.2 equiv) in toluene/hexane the lithium salt of phenylbuta-1,3-diyne is obtained and this compound is reacted in situ with electrophiles thereby forming unsymmetrically functionalized buta-1,3-diynes. Three examples using benzaldehydes as the electrophiles are included in ‌Table 8‌ (entries 12–14).[‌275‌] Additionally, the lithium acetylide intermediates may be transmetalated to provide zinc or tin derivatives and these are subsequently transformed into polyynes or arylated ynones via palladium-catalyzed cross-coupling reactions.[‌275‌]

‌Meeee 8‌ Meeeeeeee ee Meeeeeeeeeeeeee Meeeeeeeeee Meee-8,8-eeeeee eeeeeee Meeeeee–Meeeeeeeee–Meeeeeee Meeeeeeeeeeeee ee 8-Meeeeee-8,8-eeeeeeeeeeeeee[‌888‌–‌888‌]

Meeee	M8	M8	Meeee (%)	Mee
8	8-e-MeM8M8	MMM	88	[‌888‌]
8	8-MeMM8M8	MMM	88	[‌888‌]
8	8-eeeeeeee	MMM	88	[‌888‌]
8	8-eeeeeee	MMM	88	[‌888‌]
8		MMM	88	[‌888‌]
8		MMM	88	[‌888‌]
8		Me	88	[‌888‌]
8	8-MeMM8M8	Me	88	[‌888‌]
8	8-eeeeeee	Me	88	[‌888‌]
88		MMM	88	[‌888‌]
88		(M)-MM=MMMe	88	[‌888‌]
88	Me	MM(MM)Me	88e	[‌888‌]
88	Me		88e	[‌888‌]
88	Me		88e	[‌888‌]

e Meeee e eeeeeeee ee eee eeeeeee eeee ee eeeeeeeeee-8,8-eeeee eeee eee eeeeeeeeeee eeeeeeeeeeee.

Mee eeeeeeeeeeeee ee eee ee eeee eeeeeeeeeeeee eeeee eeeeee eee eeee eeeeeeee eeeee e eeeeeeeeeee eeeeee eeeeeeee eee eee eeeeeeeee ee eeeeeeee eeeeeee eeeeeeee eeeeee. Mee eeeeeee, eeee eeeeeeeeeeeeee Meeeeee–Meeeeeeeee–Meeeeeee eeeeeeeeeeeeee ee eee eeeeeeeeeeee ‌888‌ ee eee eeeeeeeee ‌888‌ (M8 = 8-eeeeeee; M8 = M) eee ‌888‌ [M8 = 8-e-MeM8M8; M8 = M(MM8)8Me] eeeeee eee eeeeeeeeeee eeeeeeee ‌888‌, ‌888‌ (M8 = 8-eeeeeee; M8 = M), ee ‌888‌ [M8 = 8-e-MeM8M8; M8 = M(MM8)8Me] ee eeeeee ee 88, 88, eee 88%, eeeeeeeeeeee (‌Meeeee 88‌).[‌888‌]

‌Meeeee 88‌ Meeeeeeeeeeeee Meee Meeeeee–Meeeeeeeee–Meeeeeee Meeeeeeeeeeeee Meeeeeee eeee eee Mee(eeeeeeeee) Meeeeeeeee[‌888‌]

Meeeeeeeeeee Meeeeeeee

8,8-Meeeeeeeeeeee-8,8-eeee-8-ee (‌Meeee 8‌, Meeee 88); Meeeeee Meeeeeeee:[‌888‌]

8.8 M MeMe ee eeeeee (8.88 eM, 8.8 eeee) eee eeeee eeeeee 8 eee (ee eeeeeee) ee 8,8-eeeeeee-8-eeeeeeeee-8-ee-8-eee (888 ee, 8.888 eeee) ee eeeeeee (8 eM) eee eeeeee (88 eM) eeee ee −88°M, eee eeeeeeeee eeeee eeeee. Mee eeeeeee eee eeeeee eeeeeee ee eeee ee 8°M, eeeeee ee eee eeeeee eeeee ee −88°M eee Me8M (88 eM) eee eeeee. MeMMM (88 ee, 8.88 eeee) ee Me8M (8 eM) eee eeee eeeeeeeeee eee e eeeeeee, eee eee eeeeeee eee eeeeeee ee eeee ee ee eeeeeeeee. Mee. ee MM8Me (88 eM) eee Me8M (88 eM) eeee eeeee, eee eeeeeee eeeee eee eeeeeeeee, eeeeee eeee eeeee (8 × 88 eM), eee eeeee (MeMM8), eee eee eeeeeee eee eeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee) ee eeee eee eeeee eeeeeeee ee ee eeeeee eeeee; eeeee: 88.8 ee (88%); ee 88–88°M.

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) M 8e, 888.