Showing papers by "Philip Magnus published in 1999"
TL;DR: The pyrylium ylide precursor 18, available in eight steps from diethyl adipate, undergoes acid catalyzed cyclization to give the cyathin derivative 4α and no detectable amount of the incorrect diastereomer 4β.
39 citations
TL;DR: In this paper, in situ generated 2-thiomethyl-2-chloro,2-phenylacetyl aryl esters with SnCl 4 (catalytic) resulted in the formation of the corresponding 3-thímethylbenzofuran-2.
30 citations
TL;DR: The ring A of taxol was synthesized from bromodiene 5 and acryloyl chloride to give 6, which was resolved by separation of diastereomers 7.
21 citations
TL;DR: A double Bischler-Napieralski reaction of the 11-membered ring carbamate 15 gave the homoannular diene 17 in a single step as mentioned in this paper.
20 citations
TL;DR: In this article, the prochiral ketone 5 was treated with the lithium salt of (+)-bis(α-methylbenzyl)amine, followed by triisopropylsilyl trifluoromethanesulfonate to give 10 (96%) β-Azidonation of 10 with (PhIO) n TMSN 3 rapidly produced 11 (95%) as a mixture of trans- and cis- diastereomers in a 3.5:1 ratio.
18 citations
TL;DR: The ABC-rings of nodulisporic acid were found to contain the structural and stereochemical elements of the ABC-ring of the aldehyde as discussed by the authors, which is the most similar structure to ours.
18 citations
TL;DR: In this paper, the 12α-hydroxyl group was replaced with a p-methoxyanilino group, which produced a dimer on attempted deprotection.
10 citations
8 citations
TL;DR: The ABC-rings of nodulisporic acid were found to contain the structural and stereochemical elements of the ABC-ring of the aldehyde as discussed by the authors, which is the most similar structure to ours.
Abstract: Lewis acid mediated cyclization of the aldehyde 7 leads to 8, 9 and 10, of which 10 contains the structural and stereochemical elements of the ABC-rings of nodulisporic acid 1.
4 citations
TL;DR: In this paper, in situ generated 2-thiomethyl-2-chloro,2-phenylacetyl aryl esters with SnCl 4 (catalytic) resulted in the formation of the corresponding 3-thímethylbenzofuran-2.
Abstract: Treatment of in situ generated 2-thiomethyl-2-chloro-2-phenylacetyl aryl esters with SnCl 4 (catalytic) resulted in the formation of the corresponding 3-thiomethylbenzofuran-2-ones.
2 citations
TL;DR: The pyrylium ylide precursor 18, available in eight steps from diethyl adipate, undergoes acid catalyzed cyclization to give the cyathin derivative 4α and no detectable amount of the incorrect diastereomer 4β.
Abstract: The pyrylium ylide precursor 18, available in eight steps from diethyl adipate, undergoes acid catalyzed cyclization to give the cyathin derivative 4α and no detectable amount of the incorrect diastereomer 4β.
TL;DR: A double Bischler-Napieralski reaction of the 11-membered ring carbamate 15 gave the homoannular diene 17 in a single step as discussed by the authors.
Abstract: A double Bischler-Napieralski reaction of the 11-membered ring carbamate 15 gave the homoannular diene 17 in a single step.
TL;DR: The cyclic hemithioacetal sulfoxide 15 readily undergoes the Pummerer reaction in the presence of carbon nucleophiles to give substituted benzylic sulfides in excellent yields as mentioned in this paper.
Abstract: The cyclic hemithioacetal sulfoxide 15 readily undergoes the Pummerer reaction in the presence of carbon nucleophiles to give substituted benzylic sulfides in excellent yields.
TL;DR: In this article, the 12α-hydroxyl group was replaced with a p-methoxyanilino group, which produced a dimer on attempted deprotection.
Abstract: Deprotection of the readily available bicyclo[7.3.1]enediyne alcohol 14 resulted in dimerization to give 18. Replacement of the 12α-hydroxyl group with a p-methoxyanilino group proceeded with overall retention to give 23 which also produced a dimer on attempted deprotection.
TL;DR: In this paper, the synthesis of pancratistatin from the prochiral ketone 1 using a chiral base to generate chiral enolate derivative is described. But this work is restricted to the case where the chirality was introduced by deprotonation with the lithium salt of (+)-bis(α-methylbenzyl)amine.
Abstract: o-Vanillin 21 was converted into 24 following literature procedures. Treatment of 24 withn-BuLi/THF followed by addition of 25 gave 26 . Dehydration (POCl 3 /pyridine/DBU), hydrogenation and hydrolysis of 26 gave the ketone 29 . Chirality was introduced by deprotonation of 29 with the lithium salt of (+)-bis(α-methylbenzyl)amine, followed by triisopropylsilyl trifluoromethanesulfonate to give 30 (95%). β-Azidonation of 30 with (PhIO) n /TMSN 3 rapidly produced 31 (95%) as a mixture of trans - and cis - diastereomers in a 3.5:1 ratio. Reduction with LiAlH 4 followed by methyl chloroformate/pyridine gave 32 , which on treatment with MCPBA/CH 2 Cl 2 /imidazole resulted in 33 . Hydrolysis of 33 gave 34 , which when exposed to KOBu t /HMPA at 90 °C resulted in 39 . After conversion of 39 into enone 42 , epoxidation with NaHCO 3 /H 2 O 2 /MeOH gave 43 . Reduction of 43 with L-selectride followed by solvolysis with sodium benzoate in water gave 46 , which was immediately acetylated to give 47 . Lactam formation (Tf 2 O/DMAP) converted 47 into 48 and the regioisomer 49 (7:1). The mixture of 48 and 49 demethylated to give 50 and the acetate protecting groups removed to give (+)-pancratistatin 1 . The synthesis of pancratistatin from the prochiral ketone 1 using a chiral base to generate a chiral enolate derivative is described. Download full-size image
TL;DR: The s-azido functionalization reaction provides a mechanistically different enone synthesis that involves treatment of 2 with fluoride anion to effect desilylation and concomitant s-elimination to give 3.
Abstract: The s-azido functionalization reaction provides a mechanistically different enone synthesis that involves treatment of 2 with fluoride anion to effect desilylation and concomitant s-elimination to give 3. Table 1 lists a number of examples of the direct conversion of a TIPS enol ether into the corresponding a,s-enone via a s-azido TIPS enol ether. The s-azido group can be ionized with Me3Al or Me2AlCl and the intermediate enonium ion trapped by a variety of nucleophiles such as an allylstannane, electron-rich aromatics, TMS enol ethers, Et2AlCN, Me2AlCCR, Me4AlLi, and vinylaluminum reagents to give the products listed in Table 2. The diastereoselectivity of the reaction of a 4-substituted enonium ion with indole shows an unusual increase of selectivity with increasing temperature. Reduction of the azide 2 provides access to s-amino TIPS enol ethers 5, which, for example, can be converted into a cinnamide derivative and cyclized via a putative “ene” process into a ?-lactam.