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Please login to access the full content or check if you have access via Variation 6: Addition of Organometallic Reagents to 1,2-Diacyl Derivatives

DOI: 10.1055/sos-SD-026-00532

Landais, Y.; Vincent, J. M.Science of Synthesis, (200526662.

Addition of organometallic reagents such as Grignard, cuprates, and organolithium to 1,2-diacyl precursors provides a straightforward route to 1,2-diketones. Oxalyl chloride is the simplest of these precursors and reacts efficiently with Grignard reagents in the presence of 1 equivalent of copper(I) bromide and, importantly, 2 equivalents of lithium bromide (Scheme 20).[‌50‌] In the absence of lithium bromide, the coupling reaction results in low conversion and a mixture of dione 70, a ketone, and a large amount of the homocoupling product results. With alkynyl precursors 71, good yields of diones 73 are obtained by addition of a solution of lithium acetylide to a suspension of 1 equivalent of copper(I) bromide and 2 equivalents of lithium bromide.[‌51‌] Better results are observed using this one-pot procedure, which generates the copper acetylide (e.g., 72) in situ, than when the freshly prepared copper acetylide is used. This suggests that lithium acetylides are more readily transmetalated by copper bromide than their magnesium counterparts, leading to a better transfer of the organic moiety from copper to oxalyl chloride. This cross-coupling reaction is thus a simple, general, and high yielding process giving access to symmetrical aryl-, heteroaryl-, and alkyl-substituted 1,2-diketones in one step from oxalyl chloride. The reaction proceeds at 0°C for aryl and alkynyl Grignard reagents and at 78°C for their alkyl counterparts. Other organometallics such as aryltrimethylsilanes react with oxalyl chloride affording 1,2-diketones in good yields.[‌52‌]

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8,8-Me(8-eeeeeee)eeeeee-8,8-eeeee (88, M8=8-Meeeeee); Meeeeee Meeeeeeee:[‌88‌]

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