Oxygenophilic organoaluminum-mediated conjugate addition of alkyllithium and Grignard reagents to quinone monoketals and quinol ethers. The directing effect of a methoxy group on the 1,4-addition process

Stern, Alan J.; Rohde, Jeffrey J.; Swenton, John S.

doi:10.1021/jo00279a033

Cited by 49 publications

(15 citation statements)

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“…The replacement of THF by ether led to extensive enolization of 15 and 18 , resulting in low-yielding conversion to addition products. The ability of methylaluminum bis(2,6-di- tert -butyl-4-methylphenoxide) (MAD) to influence facial selectivity is well recognized . However, the precomplexation of 18 with MAD did not result in a change of product composition at very short exposure times.…”

Section: Resultsmentioning

confidence: 99%

Convergent Enantioselective Synthesis of Vinigrol, an Architecturally Novel Diterpenoid with Potent Platelet Aggregation Inhibitory and Antihypertensive Properties. 1. Application of Anionic Sigmatropy to Construction of the Octalin Substructure

et al. 2003

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The coupling of building blocks 15 and 36e in the presence of MgBr(2).OEt(2) at 0 degrees C proceeds with an exo stereoselectivity (3.2:1) considerably more advantageous for the acquisition of carbinol 37e than in the absence of the additive (exo/endo = 1:5.7). The pivotal transformation that sets all of the relevant stereocenters of the cis-octalin 55 is the oxyanionic-accelerated [3,3]-sigmatropic rearrangement of 37e. A salient feature is the structurally enforced adoption of a boatlike transition state that serves to properly set four vicinal methine hydrogens in an all-cis arrangement. The ensuing conversion of 55 into iodo sulfone 62 has permitted X-ray crystallographic confirmation of all absolute stereochemical assignments since the isopropyl substituent was initially installed enantioselectively via the Evans oxazolidinone protocol. No intramolecular anionic cyclization of 62 to generate the tricyclic framework was seen. This absence of reactivity is attributed to conformational factors that inhibit attainment of the proper S(N)2 reaction trajectory.

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Section: Resultsmentioning

confidence: 99%

Convergent Enantioselective Synthesis of Vinigrol, an Architecturally Novel Diterpenoid with Potent Platelet Aggregation Inhibitory and Antihypertensive Properties. 1. Application of Anionic Sigmatropy to Construction of the Octalin Substructure

et al. 2003

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“…The critical feature in implementing this synthetic strategy was a high-yield procedure for effecting conjugate addition of organometallic reagents to quinone and quinol ketal derivatives. Until our application , of the bis(2,6-di- tert -butyl-4-methylphenoxide)methylaluminum (MAD) mediated addition of organolithium and Grignard reagents to functionalization of quinone and quinol derivatives, effecting this conversion was problematical . However, employing this conjugate addition reaction as the key step resulted in the synthesis 6c,d and 9c,d .…”

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confidence: 99%

Intramolecular Anodic Carbon−Carbon Bond Formation from Oxidized Phenol Intermediates. Effect of Oxygenated Substituents on the Yields of Spiro Dienones in Electrochemical and Iodobenzene Diacetate Oxidations

et al. 1996

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The single-cell, constant-current anodic oxidation of a series of 4-(2-alkenylaryl)phenols was studied in which the aryl substituents were 2-vinyl-4,5-dimethoxy, 6a; 2-propenyl-4,5-dimethoxy, 9a; 2-vinyl-4,5-methylenedioxy, 6b; 2-propenyl-4,5-methylenedioxy, 9b; 2-vinyl-4-methoxy, 6c; 2-propenyl-4-methoxy, 9c; 2-vinyl-5-methoxy, 6d; and 2-propenyl-5-methoxy, 9d. Two compounds having methoxyl groups on the phenolic ring were also studied: 4-(2‘-propenylphenyl)-2-methoxyphenol, 9e, and 4-(2‘-propenylphenyl)-3-methoxyphenol, 9f. A novel synthetic route to the methoxy compounds 6c, 9c, 6d, and 9d was developed. This involved as a key step the MAD, bis(2,6-di-tert-butyl-4-methylphenoxide)methylaluminum, mediated addition of organolithium and Grignard reagents to functionalize quinol ether derivatives. Anodic oxidation of compounds 6a, 9a, 9b, 6c, 9c, and 9d gave good yields of spiro dienones arising from trapping of the phenoxonium ion by the alkenyl side chain followed by reaction of the resulting cation with methanol. The products from the electrochemical oxidation of these 4-(2‘-alkenylaryl)phenols were compared with those obtained from the iodobenzene diacetate oxidations. In general, the compounds that gave good yields of spiro dienones from electrochemical oxidation gave good yields from iodobenzene diacetate oxidations. However, there were two cases in which the results of the two oxidations did not parallel each other. Whereas anodic oxidation of 9f gave a low yield of spiro dienone, the iodobenzene diacetate route gave a 74% yield of this product. In the case of 9d, the opposite effect was noted: the electrochemical route gave a higher yield than did the iodobenzene diacetate oxidation.

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“…In our hands, the use of aluminium 24 and nickel promoters 25 failed to add TMS acetylene into methoxydienone 6 . Our attention then turned toward the possibility of using quinol 9 in a ligand-assisted nucleophilic addition (LANA) reaction.…”

Section: Resultsmentioning

confidence: 70%

Torsional steering as friend and foe: development of a synthetic route to the briarane diterpenoid stereotetrad

Moon

Harned

2017

Org. Biomol. Chem.

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Two synthetic routes to the briarane stereotetrad have been investigated. The first route employed a boron aldol reaction to establish the stereogenic all-carbon quaternary carbon (C1). In this case, it was found that torsional steering in the transition state led to the formation of the undesired configuration at this position. The second route makes use of a highly diastereoselective acetylide conjugate addition/β-ketoester alkylation sequence to construct the vicinal C1 and C10 stereocenters with the correct relative configuration. Originally, it was proposed that torsional steering in the transition state for the ketoester alkylation step was the primary factor responsible for generating the major product. DFT calculations reveal that while torsional steering does play a role, larger conformational factors must also be considered. Tthese calculations also reveal that an unusual C–H•••π (alkyne) interaction may contribute to lowering the energy of one transition state that leads to the observed stereoisomer. Ultimately, this strategy leads to a concise synthesis (under 10 steps) of the stereotetrad core common to the briarane diterpenoids.

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Oxygenophilic organoaluminum-mediated conjugate addition of alkyllithium and Grignard reagents to quinone monoketals and quinol ethers. The directing effect of a methoxy group on the 1,4-addition process

Cited by 49 publications

References 0 publications

Convergent Enantioselective Synthesis of Vinigrol, an Architecturally Novel Diterpenoid with Potent Platelet Aggregation Inhibitory and Antihypertensive Properties. 1. Application of Anionic Sigmatropy to Construction of the Octalin Substructure

Convergent Enantioselective Synthesis of Vinigrol, an Architecturally Novel Diterpenoid with Potent Platelet Aggregation Inhibitory and Antihypertensive Properties. 1. Application of Anionic Sigmatropy to Construction of the Octalin Substructure

Intramolecular Anodic Carbon−Carbon Bond Formation from Oxidized Phenol Intermediates. Effect of Oxygenated Substituents on the Yields of Spiro Dienones in Electrochemical and Iodobenzene Diacetate Oxidations

Torsional steering as friend and foe: development of a synthetic route to the briarane diterpenoid stereotetrad

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