- Cyclopropanation with dibromomethane under grignard and barbier conditions
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Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnes
- Brunner, Gerhard,Eberhard, Laura,Oetiker, Juerg,Schroeder, Fridtjof
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scheme or table
p. 3708 - 3718
(2010/04/02)
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- Tandem cyclopropanation with dibromomethane under Grignard conditions
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(Chemical Equation Presented) Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and CH 2Br2 under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from α-substituted substrates, which are in accord with a staggered Houk model. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl carboxylates or vinyloxiranes. Using this methodology, numerous fragrance ingredients and their precursors were efficiently converted to the corresponding cyclopropyl carbinols.
- Brunner, Gerhard,Eberhard, Laura,Oetiker, Juerg,Schroeder, Fridtjof
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p. 7543 - 7554
(2008/12/22)
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- A short and efficient synthesis of (±)-trans-sabinene hydrate
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A short synthesis of sabinene hydrate is reported. It uses cheap starting materials and affordable reagents. The main product of the synthesis is trans-sabinene hydrate.
- Galopin, Christophe C.
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p. 5589 - 5591
(2007/10/03)
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- Allylic Lithium Oxyanionic Directed and Facilitated Simmons-Smith Cyclopropanation: Stereoselective Synthesis of (±)-cis-Sabinene Hydrate and a Novel Ring Expansion
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(matrix presented) The lithium salts of acid-sensitive allyl alcohols, which themselves decompose during Simmons-Smith cyclopropanation, undergo smooth cyclopropanation in the usual stereocontrolled manner. This concept is applied to the most efficient synthesis of (±)-cis-sabinene hydrate and to the cyclopropanation of the anion of a nonisolable allyl alcohol resulting upon workup in a ring-expanded enone. The cyclopropanations are also faster for the lithium salts than for the allyl alcohols themselves.
- Cheng, Dai,Kreethadumrongdat, Thanapong,Cohen, Theodore
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p. 2121 - 2123
(2007/10/03)
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