Sulfenium ion promoted polyene cyclizations in natural product synthesis

Harring, Scott R.; Livinghouse, Tom

doi:10.1016/s0040-4039(00)99501-7

Cited by 29 publications

(13 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…After 4 h, the reaction was diluted with ether (10 mL). Standard ethereal workup, followed by chromatography (elution with H:E, 3:2), provided 22 mg (71% for two steps) of nimbidiol acetate ( 71 ) as an off-white solid which was homogeneous by TLC analysis [H:E, 3:2, R f ( 71 ) = 0.25]: mp 158−160 °C (lit . mp 160 °C); 1 H NMR (250 MHz) δ 0.93 (s, 3 H), 0.99 (s, 3 H), 1.26 (s, 3 H), 1.48−1.85 (m, 6 H), 1.91 (dd, 1 H, J = 13.0 Hz, 5.0 Hz), 2.29 (s, 3 H), 2.30 (s, 3 H), 2.61−2.75 (m, 2 H), 7.19 (s, 1 H), 7.80 (s, 1 H); 13 C NMR (62.5 MHz) 197.6 (s), 168.2 (s), 167.8 (s), 155.0 (s), 146.4 (s), 140.4 (s), 129.6 (s), 122.4 (d), 119.2 (d), 49.1 (d), 41.1 (t), 38.2 (s), 37.8 (t), 35.9 (t), 33.3 (s), 32.5 (q), 23.4 (q), 21.3 (q), 20.7 (q), 20.6 (q), 18.7 (t) ppm.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Use of Conjugated Dienones in Cyclialkylations: Total Syntheses of Arucadiol, 1,2-Didehydromiltirone, (±)-Hinokione, (±)-Nimbidiol, Sageone, and Miltirone

et al. 1997

View full text Add to dashboard Cite

show abstract

Section: Methodsmentioning

confidence: 99%

“…Benzylic oxidation introduced the C(7) carbonyl moiety and deprotection using boron tribromide furnished nimbidiol on the basis of 1 NMR analysis. Our racemic material was acetylated prior to obtaining its 13 C NMR, IR, and mass spectra …”

Section: Synthetic Applicationsmentioning

confidence: 99%

Use of Conjugated Dienones in Cyclialkylations: Total Syntheses of Arucadiol, 1,2-Didehydromiltirone, (±)-Hinokione, (±)-Nimbidiol, Sageone, and Miltirone

et al. 1997

View full text Add to dashboard Cite

show abstract

“…Cc gave the alkylated product 7 [798 mg, 79% if the recovered starting material (780 mg) is subtracted]: !H nmr (product is numbered as a cyclized diterpene) 1.55,1.59, and 1.68 (3s,4-Me2,10-Me), 2.02 (m,4H, H-l, H-2), 2.21 (s, 3H,MeAr), 2.55 (2dd, 2H,7=13.6 and 7. 3 Hz, H-6), 3.67 (t,7=7.7 Hz, H-7), 3.82 (s, 3H, MeO), 5.06 (m, 1H, H-3), 5.16 (t, 7=7.5 Hz, H-5), 6.78 Cyclization with BF3/MeN02.-Under N2 at -30°, BF3/MeN02 (2.28 M, 3.5 ml) was added to MeN02 (5 ml), and after 2 min diene 7 (108 mg) in MeNQ2 (1 ml) was introduced. Stirring was continued at -15°for 4 h, when saturated aqueous NaHCO; was added and the product extracted into Et20.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of O-Methyl Nimbinone

Burnell¹,

Dumont²,

Théberge³

1993

J. Nat. Prod.

View full text Add to dashboard Cite

Two syntheses are described to confirm the structure 15 proposed for nimbinone. The first, which leads to racemic O-methyl nimbinone [14], involves the polycyclization of a geraniol-derived intermediate 7. This same intermediate also afforded another preparation of (±)-methyl nimbiol [12]. The other synthesis starts from natural podocarpic acid and affords optically active O-methyl nimbinone [14]. Nimbinone [15] was recently described by Ira etal. (1) as one of the constituents of Azadirachta indica, the much studied "neem" tree. This skeleton is characterized by the methyl group at C-13, which suggests that the usual isopropyl residue has been degraded in the biosynthesis.Although the method is impractical if the aromatic ring carries too many substituents(2), the synthetic approach we adapted from the Livinghouse cascade cyclization (3) should permit the ready construction of nimbinone (Scheme 1). The suitably substituted phenylacetonitrile 5 was prepared in good yield (almost 50% overall) from o-methyl anisóle[1] via the 3-formyl derivative 2 (hexamethylenetetramine, CF3COOH; 75%), the primary alcohol 3 (NaBH4, MeOH, room temperature; 94%), the benzyl bromide 4 (PBr3, pyridine, room temperature; 81%) and finally the nitrile 5 (18-cr-6, KCN, MeCN, 60°; 71%). The latter was readily alkylated with geranyl bromide [6] to afford the racemic diene 7.Cyclization of the long sidechain in the normal manner (PhSOMe, BF3/MeN02) gave the trans-fused tricyclic 8. Transformation of C-7 and then C-3 to carbonyl groups by methods found effective in our previous syntheses aimed at candelabrone (2) afforded a racemic diketone 14, which showed identical spectral properties with the same 0methyl derivative of nimbinone described by Ira et al. (1).

show abstract

“…While the presence of the β‐methoxyalkyl arylthio fragment in adducts 3 makes them potentially useful precursors for the Lewis acid induced generation of the next cationoid intermediate (ESI‐II, Scheme ), the viability of such a transformation is far from self‐evident in view of the rather poor nucleofugacity of the methoxy group. In fact, previous literature data pertinent to the ability of the methoxy group to serve as a nucleofuge in related transformations are rather scarce and refer exclusively to intramolecular cyclization reactions initiated by the generation of ESI‐like intermediates from substrates bearing appropriately positioned double bond(s) 10a,10b…”

Section: Introductionmentioning

confidence: 99%