(equilibrium mixture). Furthermore, l a acts as a pheromone, whereas 1 b is inactive. [,] Finally, cyclopentanes with cis configuration have been shown to be the biogenetic precursors of jasrnon~ids;[~' notably, this also holds true for all reduced compounds such as lactone Zrs1 and cucurbic acid (3),16] neither of which can undergo epimerization at C-2. We have now developed a synthetic strategy that makes avail- Our starting point is the asymmetric Diels-Alder reaction. Several years ago, we found that the uncatalyzed reactions of the fumarates of (8-ethyl lactate and (R)-pantolactone proceed with high diastereosele~tivity.~~~ For example, ester 4, readily available in kilogram quantities, and cyclopentadiene react with a diastereoselectivity of 98:2. The crude product is hydrolyzed with LiOH in THF/water to give the salt of 5-norbornene-2,3-dicarboxylic acid, which is then converted directly, without purification, into the iodolactone 5. Recrystallization affords enantiomerically pure['] 5 in 70-80 Yo yield. Heating a solution of the dried K salt of 5 in dimethyl sulfoxide (DMSO) (9 h, 175 "C) gives lactone 6 in 84% yield.We assume that this new cyclization is a decarboxylative 1,3 elimination. Angen. Chem. h i . Ed. Engl. 29 (1990) No. 9

No abstract

D-Galactal 1 reacts in THF in the presence of catalytic amounts of concentrated sulfuric acid to give (2R)-2-hydroxy-6,8dioxabicyclo[3.2.1]oct-3-ene (4) in a Ferrier-type rearrangement in 40% yield. When 4 is treated with diethylaminosulfur trifluoride (DAST) under certain reaction conditions, a novel intramolecular second order allylic rearrangement follows leading to previously unknown diastereomeric monofluoro derivatives 7 and 8. Direct asubstitution of 4 by DAST affords the 2-monofluoro derivative 6 under kinetic control. When DAST is used with dimethylformamide as solvent an apparent [1,3] sigmatropic migration of the 2-hydroxy group of 4 gives (4S)-4-hydroxy-6,8-dioxabicyclo[3.2.1]oct-2-ene (9). The corresponding 4-fluoro-substituted product was not obtained from the reaction of 9 with DAST. Oxidation of 4 and repeated treatment with DAST gives a novel 2,2-difluoro compound 11. Electrophilic addition of bromine to protected 4 afforded the 1,6anhydromonobromo-and-dibromohexopyranoses 15-17. Monohalo and monopseudohalo derivatives (-F,-Cl,-Br,-N 3) 22-25 were prepared by nucleophilic oxirane ring opening of the easily available endo-epoxides 18-20.

Zur weiteren Klarung der Bindungsverhaltnisse im prazedenzlosen [SIRadialenon 10 wurde eine Rontgenstrukturanalyse["I durchgefiihrt. Im Kristallgitter liegen zwei kristallographisch unabhangige Molekiile vor, die im wesentlichen die gleiche Struktur aufweisen, einschlieDlich der Konformation der terf-Butylgruppen. Abbildung 1 zeigt die Struktur von 10 im Kristall, wobei besonders der nahezu ebene Cyclopentanonring erwahnenswert ist. Die maximale Abweichung der einzelnen Atome des zentralen fiinfgliedrigen Ringes von der besten Ebene liegt bei 0.03 A. Die planare Struktur schlie5t auch die exocyclischen allenischen Doppelbindungen ein (maximale Abweichung von der besten Ebene 0.24 A). Die Bindungslangen im Carbonyl-und Al-(diese Autoren emuglen via 2 ein 6:4-Gemisch von 1 a und I b und isomerisierten es zu 1 b); b) H. Tanaka, S. Toni, J. Org. Chem. 40 (1975) 462-465;