Stereoselective total synthesis of the guaiazulenic sesquiterpenoids .alpha.-bulnesene and bulnesol

Abstract

±)-a-Bulnesene ( 39) and (±)-bulnesol (40) have been synthesized in 17 stage routes from the unsaturated keto alcohol 1. The key step involves solvolytic rearrangement of a decalyl tosylate to a hydroazulene, i.e., 38 -39 and 43 -40. The relative stereochemistry of keto ether 30, an intermediate in the synthesis of both sesquiterpenes, has been determined by correlation with dihydroeudesmol (23). The syntheses illustrate a general route to guaiazulenes which involves: (a) construction of a hydronaphthalene precurser, (b) establishment of relative stereochemistry, and (c) solvolytic rearrangement to a guaiazulene.

Mild catalytic multiphase hydrogenolysis of benzyl ethers

“…One common method for the cleavage of Bn protected hydroxyl groups is catalytic hydrogenolysis. 13 Palladium on charcoal (Pd/C) [14][15][16][17] and Raney-Ni 14,18 are among catalysts used, the solvent is generally ethanol, and the hydrogen pressures are often high for Raney-Ni. 14 Selectivity is an issue since other reduction-sensitive functional groups present in the molecule may be hydrogenated.…”

On the Origin of Siphonariid Polypropionates: Total Synthesis of Caloundrin B and Its Isomerization to Siphonarin B

“…Since caloundrin B (3) was not observed during the biomimetic synthesis of 2, 4, and 6 from the corresponding acyclic precursor (48), the synthesis of 3 should be approached using a different strategy. As an alternative, a convergent synthesis of 3 is proposed, where the γ-pyrone fragment would be coupled with a preformed trioxaadamantane fragment.…”

Access to Enantiomerically Pure Intermediates for (−)-Geosmin Synthesis Starting from (4aS,5S)-4,4a,5,6,7,8-Hexahydro-5-hydroxy-4a-methyl-naphthalen-2(3H)-one

“…8 The crude mixture containing 6c was dissolved in methylene chloride (5 ml), cooled to 09 C, and 70z perchloric acid (0.5 ml) was added. After stirring for 0.5 h at 09 C and for 2 h at room temperature, the disappearance of the starting material was conˆrmed by a TLC analysis [silica gel, developed with hexaneethyl acetate (4:1)].…”

“…8 (1S,4S,6S,8aS)-6-tert-Butyldimethylsilyloxy-1,2,3, 4,6,7,8,8a-octahydro-4,8a-dimethyl-1-thiomethylthiocarbonyloxynaphthalene (2c). To a mixture of 2b (19.7 mg, 63.4 mmol) and THF (5 ml) cooled to 09 C were added 60z sodium hydride (7.6 mg, 0.19 mmol) and imidazole (13.0 mg, 0.190 mmol).…”

“…5) We report here scalable approaches toward the reported two key intermediates [2a and 3a], 5,6) starting from (4aS,5S )-4,4a,5,6,7,8-hexahydro-5-hydroxy-4a-methylnaphthalen-2(3 H )-one (4) prepared by the reported yeast-mediated reduction of the racemic Wielnd-Miescher ketone. 7) First, according to Heathcock's procedure, 8) alcohol 4 was converted to hydroxy ketal 5. To our disappointment, stereoselective cyclopropanation with the zinc-copper couple 9) reported by Grieco and co-workers 10) was not highly reproducible.…”