Combination of RCM and the Pauson–Khand Reaction: One‐Step Synthesis of Tricyclic Structures

Abstract

The combination of ring‐closing metathesis (RCM) followed by an intramolecular Pauson–Khand reaction gives direct entry to tricyclic compounds. The RCM was carried out on a hexacarbonylcobalt‐complexed alkyne, this complex acting as a protecting group against enyne metathesis. The procedure was studied for dienynes containing heteroatoms and allows the building of [6,5,5] and [7,5,5] tricyclic systems. The feasibility of the process depends strongly on the nature of the substrate.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

(Cyclopentadienone)iron-Catalyzed Transfer Dehydrogenation of Symmetrical and Unsymmetrical Diols to Lactones

“… ,,, The selectivity of 1 – 4 for path 1 in Scheme may be due to the sterically bulky TMS groups, decreasing the rate of secondary alcohol dehydrogenation relative to primary alcohols and the irreversibility of the dehydrogenation leading to lactone formation. To gain insight into the origins of selectivity, lactol 26 (as a mixture of stereoisomers) was treated with catalysts 2 and 10 under the established reaction conditions. One equivalent of isopropanol relative to 26 was added because it would be present in solution under normal conditions after the dehydrogenation of the first alcohol.…”

“…The following (cyclopentadienone)iron carbonyl compounds were prepared by known methods: 1 and 2 , , 3 , 4 , 5 and 6 , 7 , 8 , and 9 – 12 The following diols were prepared by known methods: racemic 17a and 18a , 23a , 29a and 33a , 30a and 32a , 31a , and 34a . Lactol 26 was prepared as a mixture of stereoisomers by diisobutylaluminium hydride (DIBAL) reduction of δ-hexalactone. , …”

Synthesis of 13C‐labelled ω‐hydroxy carboxylic acids of the general formula HO213C‐(CH2)n‐CH2OH or HO2C‐(CH2)n‐13CH2OH (n = 12, 16, 20, 28)

“…After standing in the refrigerator overnight, 8a*-d* were obtained as colourless crystals, which were filtered, washed with 3-ml light petroleum and dried under reduced pressure (8a*: 216 mg, 89%; 8b*: 272 mg, 91%; 8c*: 196 mg, 93%; 8d*: 241 mg, 87%). 4.4 | Synthesis and characterization of the ω-alkenylnitriles 9a*-d* (modified after Rosillo et al 41 )…”

Iterative Synthetic Strategy for Azaphenalene Alkaloids. Total Synthesis of (−)-9aepi-Hippocasine

“…The first trial was using 1.5 molar equivalents of it, at 0 ºC (entry 5). 70 The reaction was followed by TLC and, after 20 h, no changes could be detected. In any case, the reaction mixture was filtered over silica gel and the crude residue was analyzed by 1 H NMR, showing the presence of only the starting material.…”