An enantioselective total synthesis of both enantiomers of caryophyllene-type sesquiterpenoid pestalotiopsin A has been achieved, thereby establishing the absolute stereochemistry of natural (+)-pestalotiopsin A. Highlights of the synthesis include a [2 + 2] cycloaddition of N-propioloyl Oppolzer's camphorsultam and ketene dialkyl acetal and subsequent highly stereoselective 1,4-hydride addition/protonation, an aldol reaction of functionalized bicyclic lactone with aldehyde, an efficient intramolecular Nozaki-Hiyama-Kishi (NHK) reaction for the construction of the highly strained (E)-cyclononene ring, and a palladium-catalyzed reduction of allylic mesylate with retention of the E configuration.

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The Claisen rearrangement of a spiro compound 1 derived from 1,2:5,6di-O-isopropylidene-␣-D-glucofuranose, with triethyl orthopropionate afforded the rearrangement products 4, 5, and 6 as a 1:2.5:10 diastereomeric mixture. The reaction of 1 with trimethyl orthobutyrate provided a 1:3 mixture of 7 and 8. In both cases, the -bond formation proceeded predominantly from the ␤-side. This stereochemical outcome was opposite to that observed in the case of the rearrangement of 1 with triethyl orthoacetate. ORTHOESTER CLAISEN REARRANGEMENT 59Scheme 2. Scheme 3. Downloaded by [UNAM Ciudad Universitaria] at 10:41 21 December 2014 ORDER REPRINTS inseparable mixture of 11 and 12 (20%), and 13 (72%), respectively. The mixture of 11 and 12 was treated with N-bromosuccinimide (NBS) to give a mixture of 14 and 15 in 94% yield. Compound 13 was also subjected to bromoetherification with NBS to give 16 in 97% yield. Analogously, the mixture of 7 and 8 was reduced to 17 and 18, which were readily separated by chromatography on silica gel. The bromoetherification of 17 or 18 provided 19 or 20 in overall yield of 20% or 64%, respectively, from the mixture of 7 and 8. The structures of the conformationally rigid compounds 14-16, 19 and 20 were determined by 1 H NMR analysis that included NOE difference experiments (Figure 2). In the NOE difference experiments 60 TAKAO, SAEGUSA, AND TADANO Scheme 4. Scheme 5.

Stereoselective Carbon-Carbon Bond Forming Reactions of Chiral Cyclopent-2-enone and Cyclopentene-1-methanol, Both Spiroconnecting a 1,2:5,6-Di-O-isopropylidene-α-D-glucofuranosyl Ring.-The conjugate addition reactions of various organocopper reagents [cf. (II) and (V)] as well as dimethyl malonate anion (VIII) to title cyclopentenone (I) are studied, and for most cases the optimal conditions are found, which provide the corresponding β-functionalized cyclopentanones in high to excellent diastereoselectivity. Additionally, the reaction of spirocyclic hydroxymethylcyclopentene (XI) with triethyl orthoacetate (XII) proceeds by a thermal Claisen rearrangement to provide spirocyclic methylenecyclopentylacetic acid ester (XIII) in high diastereoselectivity (87% d.e.). -