Journal
TETRAHEDRON
Volume 67, Issue 27-28, Pages 5011-5023Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2011.03.116
Keywords
Achmatowicz; Asymmetric; Cyanohydrin; Diastereoselective; Oxy-Michael
Categories
Funding
- University of Oxford
- EPSRC
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We describe efforts to achieve a multigram synthesis of the tricyclic spiroacetal core of the lituarines based on the addition of acyl anion equivalent to 4-(2-furyl)butan-2-one (18). We report the first cases of chemoselective Achmatowicz reaction in the presence of a second furan ring that lacks an alpha-hydroxyl group. The use of lithiated methoxyallene provides an efficient one-step conversion of ketone 18 into a tricyclic Diels-Alder adduct (27). In the final route, asymmetric cyanosilylation of ketone 29 achieved the construction of the stereogenic C(12) 3 degrees-alcohol centre. Subsequent butenylation, diastereoselective reduction of keto-alcohol (+)-33 and alkene cross metathesis set up an oxy-Michael reaction to close the C(8-12) tetrahydropyran ring. The second ring-closure, which completed the route, was achieved by oxidative spirocyclisation following our earlier work. (C) 2011 Elsevier Ltd. All rights reserved.
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