Science of Synthesis

Gandon, V.; Malacria, M., Science of Synthesis, (2008) 44, 215.

1-Chlorovinyl 4-tolyl sulfoxides such as ‌105‌ are readily available from ketenes in three steps using chloromethyl 4-tolyl sulfoxide.[‌143‌] A magnesium–sulfoxide exchange reaction allows the formation of a (1-chlorovinyl)magnesium species, which can also be depicted as an alkylidene carbene ‌106‌.[‌104‌,‌143‌–‌145‌] Treatment of these carbenoids with α-sulfonyl carbanions gives allenes, e.g. ‌108‌, in moderate to good yields (‌Scheme 63‌). Overall, this three-component process involving ketones, chloromethyl 4-tolyl sulfoxide, and sulfones allows the rapid construction of tri- and tetrasubstituted allenes. Optimized reaction conditions can be summarized as follows: tert-Butylmagnesium chloride (0.5 equiv) does not react with sulfoxides but is used to remove traces of moisture from tetrahydrofuran in order to avoid the fast reaction of the carbenoid with water; the sulfoxide magnesium–exchange is achieved in one minute by either ethylmagnesium chloride or isopropylmagnesium chloride (3 equiv) keeping the temperature at −78°C, otherwise significant degradation of the carbenoid occurs. A solution of a lithium α-sulfonyl carbanion (3 equiv) is added at −78°C; this anion attacks the electron-defficient carbon and the resulting vinyl anion, e.g. ‌107‌, undergoes β-elimination of the sulfonyl group to give the allene.

‌Meeeee 88‌ Meeeeeeee ee ee Meeeee eee ee Meeeeeeeeeeeeeeeeeeee Meeeeeeeeeee[‌888‌]

Meeeeee eeeeeeee eeee eeee eeeeee eeee eee 8-eeeeeeeeeee 8-eeeee eeeeeeeee ‌888‌ (‌Meeeee 88‌). Meeeeeeeeeeee, ee eeeeeeee ee eeeeeeeee eeeeee eeeeee eeeeeee, α-eeeeeeee eeeeeeeeee eeeeeee eeee eeeeee ee eeeee eeeeee eeeeeeee eeee eee eeeeee ee eeeeeee eeeeeeee.

‌Meeeee 88‌ Meeeeeeee ee Meeeeee eeee e 8-Meeeeeeeeee 8-Meeee Meeeeeeee eee Meeeeee α-Meeeee Meeeee Meeeeeee[‌888‌]

‌Meeeeeeeeee 88‌

e Meeeeee eeeeeee.

Meee eeeeee (eee eeee eeeeeeeeeee) eee eeeeeee eeeeeee eee eeee eeee ee eee eeeeeee (‌Meeeee 88‌). Mee eee eeeeeeeeeeeeee ee eeeeeeeee ‌888‌ [M8,M8 = (MM8)88] eeeeeee eeee eeeeeeeeeeeeeeeeee, eeeeeeeeeeeeeeeeeeee eeeeeeee ee eeee ee ee eeeeeeee.

‌Meeeee 88‌ Meeeeeeee ee Meeeeee eeee 8-Meeeeeeeeee 8-Meeee Meeeeeeeee eee Meeeeee α-Meeeee Meeeee Meeeeeee[‌888‌]

‌Meeeeeeeeee 88‌

e MMMM eeee ee eeeeeeee.

Me eeeeeeee eeee eee eeeeeeeee, ee eeeee e eeeeeeeee eeeeeeeeeeee eeee ee eeeeee eeeeeeeeeee ee eeeeeeee, eeeeee-ee-eeee eeeeeeeee eeeeeeee eeee ee eeeeeeeee eeeeee eeeeeeeee eeeee: eee eeeeeeeee eeeeee ee eeeeee ee e eeeeeeee.

Meeeeeeeeeee Meeeeeeee

8-(Meeeeeeeeeeeeeee)-8,8-eeeeeeeeee[8.8]eeeeee (‌888‌); Meeeeee Meeeeeeee:[‌888‌]

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References