A new conversion method from (-)-limonene to nepetalactones.

Preparation of (5R)-4,8-dimethylbicyclo[3.3.0]oct-1(8),3-dien-2-one from (-)-limonene oxide: a novel intermediate to the synthesis of 4-5-5 fused tricarbocyclic core present in terpenic natural products

“…[21][22][23] Running the hydrogenation reaction with the same catalyst at 810 kPa of hydrogen pressure in EtOH at 25 o C, for 24 h, gave a mixture of the saturated ketone 16 and a minor saturated product which was not separable by chromatography on silica gel. The structure of 16 was supported by the assignments of its 1 H and 13 C NMR data and comparison with those described in the literature 24 while the minor saturated component which was not fully characterized in this work is presumably formed by the addition of hydrogen from the more sterically encumbered face of (-)-6.…”

Stereoselective Total Synthesis of Leiocarpin C and (+)-Goniodiol

“…The cyclization of cis-a,b-unsaturated ester 8 was achieved via intramolecular lactonization to afford (+)goniodiol in 60% yield after sequential removal of silyl and acetonide protecting groups using a catalytic amount of 4-toluenesulfonic acid in methanol. 13 The synthesis of leiocarpin C was initiated by replacing the tert-butyldimethylsilyl group with methoxymethyl protection in alcohol 10 to avoid the steric hindrance gen-erated by the TBS group (Scheme 3). After that, debenzylation of the MOM product 11 was achieved by using DDQ/H 2 O, 11 which was further oxidized to afford an aldehyde using IBX/DMSO.…”

“…15 The resulted methyl ester 14 was cyclized through an intramolecular lactonization in a single step using a catalytic amount of 4-toluenesulfonic acid in methanol to afford leiocarpin C in 70% yield. 13 The fragment 9 was prepared from a chiral C 2 -asymmetrical diol which in turn was derived from readily available (-)-diethyl D-tartarate (Scheme 4). 16 Monoprotection of the diol was achieved with tert-butyldimethylsilyl chloride in the presence of sodium hydride to give the TBS ether 15 in 95% yield.…”

Transition Metal-Catalyzed Carbocyclizations in Organic Synthesis

“…The effects of various Rh(I) catalyst species and reaction variables on this process has been extensively investigated and much attention has been drawn to its possible mechanisms, − stereoselectivity, and applications to the syntheses of natural products. − This process initially suffered from low yields and small turnover of catalyst species except for using ethylene as the additive, but later high turnovers were achieved by heating or by using dirhodium complexes as the catalysts. − …”