Acetylide additions to enediones. Regioselectivity based on stereoelectronic control

Liotta, Dennis; Saindane, Manohar; Sunay, Ustun B.; Jamison, W.C.L.; Grossman, Jan; Phillips, Pamela

doi:10.1021/jo00217a055

Cited by 24 publications

(11 citation statements)

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“…Beim Epoxy-Diketon 18 reagiert diese Position ebenfalls bevorzugt. Als Grund fur eine solche Selektivitat wird eine Bevorzugung eines axialen Angriffs des entsprechenden Anions angenommen [8]. Das Tab.…”

Section: The Synthesis Of the Labdane Diterpenoid Erigerol And Of Anaunclassified

“…rac -3ua - 6p,6ub,7,8,9,9ua, -ethinyl-4u,8'ua-dihydro-S-hydro~y-4ua,6-dimethylspiro(an-l,l 4,4u,5,6.7,8,8ua-octuhydro-4-hydroxy-3,4ua,8,~-tetrumrthylnuphthulin-l(4H/-on 5,6,7,8,8aa -octuhydro-4~-hydroxy-4-(3a/3,!&hydroxy-3- -5,5-dimet/zo,~y-3-m~thyl-3-[/trimethylsil,vl) Reduktion uon 79 rnit NuBH4, LiCI, Li2C0,. NaBH, (9,42 g ,0,25 mol) und H20-freies LiCl(103 g; 0,25 mol) wurden 1 h bei RT.…”

Section: 7'8'8u-octahydro-2'55's8u~-pentamethylspiro[furan-2[unclassified

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Die Synthese des Labdanditerpenes Erigerol und analoger Verbindungen

Kienzle

Stadlwieser

Rank

et al. 1990

Helvetica Chimica Acta

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Section: The Synthesis Of the Labdane Diterpenoid Erigerol And Of Anaunclassified

Section: 7'8'8u-octahydro-2'55's8u~-pentamethylspiro[furan-2[unclassified

Die Synthese des Labdanditerpenes Erigerol und analoger Verbindungen

Kienzle

Stadlwieser

Rank

et al. 1990

Helvetica Chimica Acta

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“…While the conversion of Z to la was readily accomplished using platinum black in ethanol, attempts to desilylate U with a variety of different fluoride sources resulted in the formation of multiple products, the major component of which was indeed pallescensin A, a.At this juncture one might legitimately wonder why a trimethylsilylsubstituted furan was employed at all in the synthesis. In fact, unless the furan ring in question is at least disubstituted, we have shown in other studies that Lindlar reductions of fury1 acetylenes result primarily in the formation of tetrahydrofuryl olefins 9. The attempted reduction of the desilylated analog of 5 did not prove to be an execption to this mle!…”

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confidence: 72%

Triene Cyclizations. The Total Synthesis of Pallescensin A

Liotta

Ott

1987

Synthetic Communications

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The total synthesis of pallescensin A has been achieved using a six x , thermal electrocyclization reaction as the key step.Pallescensin A, is a furanosesquiterpenoid marine natural product isolated from the sponge Disidea pallescens.l It is postulated to be involved in the chemical defense mechanism of the opisthobranch molluscs, which concentrate sponge metabolites in their skin glands and, when in danger, employ them in defensive secretions.2There have been a number of syntheses of pallescensin A reported at the time of this writing (vide infra). Three of these approaches make use of cationic cyclizations between a furan and one or more olefin units3 and generally suffer from the fact that both cis-and transring junctures are produced during the cyclizations. A second type of approach relies on a phenoVfuran interconversion whose key step is the ozonolysis of an extensively-modified derivative of dehydroabietic acid.4 Finally, the most 1655 1656 LIOTTA AND OTT recent approach involves the conversion of enantiomerically-pure Wieland-Miescher ketone to a decalone keto aldehyde, which is then transformed to 1 via a cyclization/dehydration sequence.5 Nasipun et al p 0In this communication we wish to report our approach to the total synthesis of pallescensin A which utilizes a thermal, six II: electrocyclization of furanodiene 6 as its key step (see Scheme I).Intermediate 6 was prepared in three steps from compounds j! and 3.6Addition of furylacetylide 3 to trimethylcyclohexanone, 2, resulted in the formation of acetylenic alcohol 4, which was isolated in a pure enough state to be used without further purification. Exposure of this material to boron trifluoride etherate resulted in clean dehydration to produce 5 in 77% overall yield from 2 and 3. Lindlar hydrogenation of 5 proved to be problematic. If the reaction was allowed to proceed until all the starting material was consumed (as monitored by TLC), then significant amounts of overreduction products were observed. This problem was circumvented by allowing the reduction to only proceed to 50%completion. The starting material and product could then be easily Downloaded by [University of Chicago Library] at 19:50 16 November 2014 1657 TRIENE CYCLIZATIONS separated by silica gel chromatography. Using this approach, no other side products were observed and the starting material could be recycled in subsequent runs. The thermolysis of 6 was carried out in a sealed tube with either benzene of toluene as a solvent. (Note: if deuterobenzene was used in place of benzene, the reaction could be carried out in a sealed NMR tube and monitored by NMR.) Thermolysis temperatures typically ranged from 1600 to 200OC. If the temperature of the thermolysis exceeded 21 OOC, then large amounts of unidentified by-products were obssnred. Scheme I 5 6 z Scheme II I F I Downloaded by [University of Chicago Library] at 19:50 16 November 2014 1658 LIOTTA AND OTTA number of features of the key cyclization step are noteworthy.First, according to the Woodward-Hoffman rules, 5 should undergo t...

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“…In contrast, diketones OPEN ACCESS need to be selectively protected with ethylene glycol before the alkynylation [13]. Liotta reported a useful method for preparing highly functionalized synthetic intermediates without the use of protecting groups based on stereoelectronic control [14], but the conditions of these reactions were harsh. As part of our continuing interest in the synthesis and bioactivities of 1-ethynylcyclohex-2-enol derivatives, a series of 1,4-enediones with high steric effects including substituted six-membered rings, tetralones, and quinolines were selected to react with a range of acetylides.…”

Section: Introductionmentioning

confidence: 99%

“…The regioselectivity of these acetylide additions can be determined using a variety of techniques, the simplest of which is proton NMR. Since the products of these additions are enones, it is quite a straightforward matter to determine if the material in question possesses an α-enone proton (high field) or a β-enone proton (low field) [14]. In 2a, because of the dual effect of the 7′-methyl electron-donating effect and the α,β-unsaturated ketone conjugate effect, the α-H tends toward the 1 H-NMR low field.…”

Section: Introductionmentioning

confidence: 99%