Abstract
A series of 1-heteroatom-substituted vinyl p-tolyl sulfoxides were prepared and treated with organometallic reagents to evaluate which combination of sulfoxides and organometallic reagents yielded alkynes the most efficiently. The use of 1-chlorovinyl p-tolyl sulfoxide and isopropylmagnesium chloride was optimal for this purpose. A variety of 1-chlorovinyl p-tolyl sulfoxides were prepared from carbonyl compounds and chloromethyl p-tolyl sulfoxide and were converted into alkynes via the sulfoxide/magnesium exchange reaction and subsequent Fritsch–Buttenberg–Wiechell (FBW) rearrangement of the resulting magnesium alkylidene carbenoids. The mechanism of the FBW rearrangement of magnesium alkylidene carbenoids was studied by using 13C-labeled sulfoxides and by using DFT calculations.
Highlights
Alkynes are important compounds in organic synthesis [1]
As magnesium alkylidene carbenoid precursors, a series of 1-heteroatom-substituted vinyl p-tolyl sulfoxides 2, 5–7 and 1-unsubstituted sulfoxide 8 were prepared from carbonyl compounds 1 (Scheme 3)
The 1-bromovinyl p-tolyl sulfoxide 6 was prepared by the deprotonation of sulfoxide 8 with LDA followed by electrophilic bromination with 1,2dibromo-1,1,2,2-tetrachloroethane. 1-Methoxyvinyl p-tolyl sulfoxide 7 was prepared by a Peterson olefination of 4,4'dimethoxybenzophenone with methoxy(trimethylsilyl)methyl p-tolyl sulfide, and oxidation of the resulting 1-methoxyvinyl p-tolyl sulfide with mCPBA (Scheme 3b) [17]
Summary
Alkynes are important compounds in organic synthesis [1]. Electrophilic additions of alkynes give functionalized compounds, and cycloadditions such as the Huisgen reaction afford cyclic compounds. We report the synthesis of alkynes 4 from carbonyl compounds 1 with one-carbon homologation via the FBW rearrangement of magnesium alkylidene carbenoids 3 as a key step. Magnesium alkylidene carbenoids 3 can be generated from isopropylmagnesium chloride and 1-chlorovinyl p-tolyl sulfoxides 2, which are prepared from carbonyl compounds 1 and chloromethyl p-tolyl sulfoxide, via the sulfoxide/magnesium exchange reaction [11].
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