Protodesilylation of allylsilanes for the control of double bond geometry exocyclic to a ring

Fleming, Ian; Higgins, Dick

doi:10.1039/p19920003327

Cited by 10 publications

(7 citation statements)

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“…We were able to show that protodesilylation of the allylsilane 41, which had a similar level of substitution at both ends of the allylic system to that of the allylsilane 39, gave the E-double bond in the product 42 with high selectivity in the desired sense (Scheme 9), and have published this result. 3 But, in the present work, we have been unable to use our synthesis of an allylsilane in the general sense 38 39. The model carbamate 43, having a substitution pattern with branching adjacent to both ends of the allylic system, simply failed to react (Scheme 9), a limitation that had not been evident in our exploratory work with less highly substituted systems.…”

Section: The a ؉ Bc Coupling Strategymentioning

confidence: 81%

Stereocontrol in organic synthesis using silicon-containing compounds. Studies directed towards the synthesis of ebelactone AElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/ob/b3/b316899a/

et al. 2004

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Several approaches to the synthesis of ebelactone A 2 are described, culminating in the synthesis of the benzenesulfonate of 2-epi-ebelactone A 161. All the approaches were based on three fragments A, B and C, originally defined in general terms in, but eventually used as the aldehyde 72, the allenylsilane 3 and the aldehyde 139, respectively. They were joined, first B with C, and then B+C with A. In the main routes to fragments A and C, the relative stereochemistry was controlled by highly stereoselective enolate methylations 67-->67, 68-->69, and 135-->136, in each case anti to an adjacent silyl group, and by a highly stereoselective hydroboration of an allylsilane 137-->138, also anti to the silyl group. The hydroxyl groups destined to be on C-3 and C-11 were unmasked by silyl-to-hydroxy conversions 69-->70 and 138-->139 with retention of configuration. The stereochemistry created in the coupling of fragment B to C was controlled by the stereospecifically anti S(E)2' reaction between the enantiomerically enriched allenylsilane 3 and the aldehyde 139. The double bond geometry was controlled by syn stereospecific silylcupration 148-->151, and preserved by iododesilylation 151-->152 of the vinylsilane with retention of configuration, and Nozaki-Hiyama-Kishi coupling with the aldehyde 72 gave the whole carbon skeleton 153 of ebelactone A with the correct relative configuration, all of which had been controlled by organosilicon chemistry. In the steps to remove the superfluous allylic hydroxyl, an intermediate allyllithium species 156 abstracted the proton on C-2, and its reprotonation inverted the configuration at that atom. Other routes to the fragments A and C were also explored, both successful and unsuccessful, both silicon-based and conventional, and a number of unexpected side reactions were investigated.

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Section: The a ؉ Bc Coupling Strategymentioning

confidence: 81%

Stereocontrol in organic synthesis using silicon-containing compounds. Studies directed towards the synthesis of ebelactone AElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/ob/b3/b316899a/

et al. 2004

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“…If the reaction was allowed to continue for longer periods of time 19 did slowly isomerize to the endocyclic isomers. Thus electrophilic attack on the terminal disubstituted alkene is faster than attack on the conjugated alkene, and the deactivating effect of the ester must be greater than the activating effect of the allylic trimethylsilyl group (20).…”

Section: Mecumentioning

confidence: 99%

The synthesis of the isomeric components of San Jose scale pheromone — an illustration of a stereospecific synthesis of trisubstituted alkenes

Alderdice¹,

Spino²,

Weiler³

1993

Can. J. Chem.

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The three isomeric components of the San Jose scale pheromone, 5-7, have been synthesized from a common P-keto ester intermediate. A study of the alkylation of the dianion of methyl acetoacetate with a series of alkylating agents with the same carbon skeleton has been carried out. The trisubstituted alkenes in 5 and 6 have been synthesized stereospecifically via a copper-catalyzed coupling of a methyl Grignard reagent with the E or Z en01 phosphate from the alkylated P-keto ester. In the case of the Z en01 derivative, the coupling reaction was carried out on the diethyl-and diphenylphosphates, and the en01 triflate. 'The diethyl en01 phosphate gave the highest stereoselectivity. The synthetic pheromones were attractive to San Jose scale in the field.MARGOT ALDERDICE, CLAUDE SPINO et LARRY WEILER. Can. J. Chem. 71, 1955Chem. 71, (1993. Utilisant un p-ceto ester commun comme intermediaire, on a synthetise les trois isomitres 5-7 de la pheromone du pou de San JosC. On a rCalisC une Ctude de I'alkylation du dianion de 1'acCtoacetate de mCthyle par une sCrie d'agents d'alcoylation ayant le m&me squelette carbone. On a synthCtisC les alcitnes trisubstituCs 5 et 6 d'une maniitre stCreospCcifique en faisant appel a un couplage catalysC par le cuivre d'un mCthyl magnesien avec le phosphate d'Cnol E ou Z obtenu B partir du p-ceto ester alcoyle. Dans le cas du dCrivC Cnolique Z, on a rCalisC la reaction de couplage sur les phosphates Cnoliques diCthyle et de diphenyle et sur le triflate Cnolique. Le phosphate Cnolique diethylique donne la meilleure sterCosClectivitC. Dans les champs, les phCromones de synthitse attirent le pou de San Jose.[Traduit par la redaction]

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“…Protodesilylation of allylsilanes has been used to control exocyclic double-bond geometry. The allylsilane 193 gave largely (91:9) the ( E )-alkene 194 , and its regioisomer 195 gave largely (92:8) the ( Z )-alkene 196 (Scheme ) . This device was used to control the exocyclic double-bond geometry to better than 96:4 in a synthesis of a carbacyclin 198 by protodesilylation of the allylsilane 197 (Scheme ).…”

Section: Electrophilic Attack On Allylsilanesmentioning

confidence: 99%

“…Similarly, the protodesilylations of the allylsilanes 193 and 195 in Scheme are stereoselective in the control of the double-bond geometry only when the substituent on the stereogenic center is a large group like isopropyl. When the substituent is only a methyl group the selectivity for the exocyclic double-bond geometry is much less . Changing the double bond in the starting material from trans to cis has the same effect, and for the same reason (Scheme ). ,, The diol 221 is the major product from the cis -allylsilane 220 , and hence the cis -alkene 218 is the major alkene derived from it, even when R is a methyl group.…”

Section: Electrophilic Attack On Allylsilanesmentioning

confidence: 99%

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

1997

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Protodesilylation of allylsilanes for the control of double bond geometry exocyclic to a ring

Abstract: Protodesilylation of the allylsilanes 5 and 6 is selective for the formation of the exocyclic double bond isomers 7 and 8, respectively, when the group R is isopropyl, but not when it is methyl.

Cited by 10 publications

References 4 publications

Stereocontrol in organic synthesis using silicon-containing compounds. Studies directed towards the synthesis of ebelactone AElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/ob/b3/b316899a/

Stereocontrol in organic synthesis using silicon-containing compounds. Studies directed towards the synthesis of ebelactone AElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/ob/b3/b316899a/

The synthesis of the isomeric components of San Jose scale pheromone — an illustration of a stereospecific synthesis of trisubstituted alkenes

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

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