“…Transformation of enol triflate 17 to the desired vinyl bromide 18 was achieved by successive treatment with Me 3 SnSnMe 3 and Br 2 by the Wulff protocol . Finally, crucial diimide reduction of vinyl bromide 18 from the less hindered convex face, as shown in conformation E , delivered the desired bromide 19 in a highly stereoselective fashion. 5 Introduction of Bromine at C(9) of (+)-Isolaureatin ( 1 ) a a Reagents and conditions: (a) CBr 4 , Oct 3 P, toluene, rt to 80 °C, 4 h, <10%; (b) TPAP, NMO, CH 2 Cl 2 , rt, 3 h, 92%; (c) KHMDS, THF, −78 °C, 30 min, then PhNTf 2 , −78 °C, 1 h, 94%; (d) i.…”
The first asymmetric total syntheses of the dihalogenated medium-sized dioxabicyclic marine natural products (+)-3-(Z)-isolaureatin (1) and (+)-3-(Z)-laureatin (2) have been accomplished. Notable features of the highly stereo-, regio-, and chemoselective syntheses of these alpha,alpha'-trans-oxocene natural products include an intramolecular amide enolate alkylation to construct the alpha,alpha'-cis-oxocene, novel "lone pair-lone pair interaction-controlled" epimerizations to the alpha,alpha'-trans-oxocenes, various strategies for stereoselective introduction of halogen atoms, and novel olefin cross-metatheses for construction of the (Z)-enyne systems.
“…Transformation of enol triflate 17 to the desired vinyl bromide 18 was achieved by successive treatment with Me 3 SnSnMe 3 and Br 2 by the Wulff protocol . Finally, crucial diimide reduction of vinyl bromide 18 from the less hindered convex face, as shown in conformation E , delivered the desired bromide 19 in a highly stereoselective fashion. 5 Introduction of Bromine at C(9) of (+)-Isolaureatin ( 1 ) a a Reagents and conditions: (a) CBr 4 , Oct 3 P, toluene, rt to 80 °C, 4 h, <10%; (b) TPAP, NMO, CH 2 Cl 2 , rt, 3 h, 92%; (c) KHMDS, THF, −78 °C, 30 min, then PhNTf 2 , −78 °C, 1 h, 94%; (d) i.…”
The first asymmetric total syntheses of the dihalogenated medium-sized dioxabicyclic marine natural products (+)-3-(Z)-isolaureatin (1) and (+)-3-(Z)-laureatin (2) have been accomplished. Notable features of the highly stereo-, regio-, and chemoselective syntheses of these alpha,alpha'-trans-oxocene natural products include an intramolecular amide enolate alkylation to construct the alpha,alpha'-cis-oxocene, novel "lone pair-lone pair interaction-controlled" epimerizations to the alpha,alpha'-trans-oxocenes, various strategies for stereoselective introduction of halogen atoms, and novel olefin cross-metatheses for construction of the (Z)-enyne systems.
A general method for the selective hydrogenation of alkenyl halides to alkyl halides is described. Fluoro, chloro, bromo, iodo, and gem-dihaloalkenes are viable substrates for the transformation. The selectivity of the hydrogenation is consistent with reduction by a hydrogen atom transfer pathway.
This article reviews the progress in the chemistry of the steroids that was published between January and December 2003. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 152 references.
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