Diastereoselectivity in the SE2? reaction of chiral pentadienylsilanes: a test for the relative importance of steric and electronic effects

Fleming, Ian; Jones, Graeme R.; Kindon, Nicholas D.; Landais, Yannick; Leslie, Colin P.; Morgan, Ian T.; Peukert, Stefan; Sarkar, Achintya Kumar

doi:10.1039/p19960001171

Cited by 17 publications

(34 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We converted the same mixture of the syn alcohols 31 into the Mosher's esters 35 and 36, which were also present in a ratio of 99 : 1 (Scheme 7). All of the possible stereoisomers of these Mosher's esters were already known to us, with assigned relative and absolute configurations, 41 confirming that the S E 2Ј reaction of the allenylsilane is indeed stereospecifically anti, as well as being to a very high degree. This work confirmed that the major product 35 was the isomer with the syn relationship between C-2 and C-3, and hence that the reaction with the allenylsilane had given the homopropargylic alcohol (3R,4R)-31 with the syn relationship between C-3 and C-4.…”

Section: Electrophilic Substitution Reactions Of the Allenylsilane 29supporting

confidence: 64%

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

et al. 2004

Self Cite

View full text Add to dashboard Cite

The allylsilanes, (R)-E- and (R)-Z-4-trimethylsilylpent-2-ene 16, were prepared in essentially an enantiomerically and geometrically pure state (er >99.95 : 0.05, E : Z and Z : E >99.95 : 0.05) by, successively, conjugate addition of lithium dimethylcuprate to N-[(E)-3'-trimethylsilylpropenoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide 13, to give N-[(E)-(3'R)-3'-trimethylsilylbutanoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide, removal of the chiral auxiliary with bromomagnesium benzyloxide, aldol reaction with acetaldehyde, and decarboxylative elimination, to give either the Z- or E-isomer. Both the E- and Z-allylsilanes 16 reacted with the adamantyl cation to give mixtures of E- and Z-4-adamantylpent-2-enes 17. The E-allylsilane gave the E- and Z-products in a ratio of 40 : 60, and the Z-allylsilane gave the E- and Z-products in a ratio of 99.8:0.02. The enantiomer ratio was >99:1 for the reaction of the E-allylsilane giving the Z-product, 90:10 for the E-allylsilane giving the E-product, and 95 : 5 for the Z-allylsilane giving the E-product, showing that the reactions were stereospecific to a high degree, but not always quite completely so. The allenylsilane, 2-trimethylsilylpenta-2,3-diene 29, was prepared enantiomerically highly enriched (er 99:1) by copper-catalysed reaction of methylmagnesium chloride with (S)-4-trimethylsilylbut-3-yn-2-yl camphor-10-sulfonate 28. The allenylsilane 29 reacted with the adamantyl cation to give (S)-4-adamantylpent-2-yne (S)-30 with the same level of enantiomeric purity, showing that the reaction was, as accurately as can be measured, completely stereospecific. The allenylsilane 29 also reacted with isobutanal in the presence of titanium tetrachloride to give 2,4-dimethylhept-5-yn-3-ol as a mixture of diastereoisomers, syn 31 and anti 32, in a ratio of 95:5, with the major diastereoisomer present as a mixture of enantiomers (4R,5R):(4S,5S) in a ratio of 99:1, showing that the reaction was, as accurately as can be measured, completely stereospecific in the anti sense. The corresponding propargylsilane, 4-trimethylsilylpent-2-yne 37, reacted with the adamantyl cation to give dienes assigned the structures 2,3-diadamantyl-1,3-pentadiene 42 and 2,4-diadamantyl-1,3-pentadiene 43, and reacted with isobutanal in the presence of titanium tetrachloride to give 2-(1-hydroxy-2-methylpropyl)-3-trimethylsilylpenta-1,3-dienes 45 and 2,4-dimethyl-5-trimethylsilylhept-5-en-3-one 46. The enantiomerically enriched propargylsilane (R)-1,3-bis(trimethylsilyl)but-1-yne (er >99.7:0.3) was prepared from the sultam 13, by removal of the chiral auxiliary with lithium ethoxide, reduction of the ethyl ester to give (R)-3-trimethylsilylbutanal 60, enol triflate formation, beta-elimination and C-silylation. The propargylsilane reacted with 2,4-dinitrobenzaldehyde in the presence of titanium tetrachloride to give the allenes, 1-(2,4-dinitrophenyl)-2-trimethylsilylpenta-2,3-dienols 63-66, as two diastereoisomers in a ratio of 2 : 1, each of whi...

show abstract

Section: Electrophilic Substitution Reactions Of the Allenylsilane 29supporting

confidence: 64%

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

et al. 2004

Self Cite

View full text Add to dashboard Cite

show abstract

“…site-''unrelayed'' 1,5-stereocontrol with a selectivity of 90 : 10 has been described as ''remarkable''. 9 This review will consider cases where stereocontrol over at least seven bond lengths-which typically amounts to a linear distance of ca. 1 nm-has been achieved.…”

Section: Jonathan Claydenmentioning

confidence: 99%

Transmission of stereochemical information over nanometre distances in chemical reactions

Clayden

2009

Chem. Soc. Rev.

109

View full text Add to dashboard Cite

By exploiting intramolecular interactions such as dipole repulsion, and by incorporating a terminal chiral controlling feature, the global conformation of a molecule may be governed. In such an environment, stereoselective reactions can occur at considerable distances from the source of stereochemical information, providing a simple method for information relay over scales of >1 nm (or about seven bond lengths). This tutorial review discusses the development of this idea, and describes examples which depend on relayed dipole repulsion and on the absolute control of helicity. Future prospects in the area employing control over extended helical foldamers are elaborated.

show abstract

“…[2] To what extent this stereocontrol is steric or electronic in origin remains a matter of debate, in spite of studies which have carefully addressed this problem. [17] Conformation IVb, with the medium-sized group R M inside, experiences strong A 1,3 interactions between R M and R Z , thus explaining the generally higher diastereocontrol observed with (Z)-allylsilanes than with (E)-allylsilanes. [2,3] In cyclic systems, locked conformations provide sufficient Figure 4.…”

Section: Introductionmentioning

confidence: 95%

Allylsilanes in Organic Synthesis − Recent Developments

2004

Self Cite

View full text Add to dashboard Cite

show abstract

Diastereoselectivity in the SE2? reaction of chiral pentadienylsilanes: a test for the relative importance of steric and electronic effects

Cited by 17 publications

References 54 publications

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

Accurate determinations of the extent to which the SE2? reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

Transmission of stereochemical information over nanometre distances in chemical reactions

Allylsilanes in Organic Synthesis − Recent Developments

Contact Info

Product

Resources

About