“…Thus, organoaluminium reagents can be used to desymmetrise sulfinylquinols by a diastereoselective conjugate addition to the enone fragment of the quinol 183 (Scheme 83). 151 A variety of alanes can be used and in all the cases described, only one single diastereoisomer is obtained. …”
Chiral sulfinyl groups have been widely used in organic synthesis as a stereo-and enantiodirecting functionality and the high efficiency of the selectivity has received much attention in recent years. In this review we wish to cover the work published in the literature since 1996. The participation of a chiral sulfinyl function in a wide range of reactions as well as the application of these methodologies to the synthesis of natural products are reported.
“…Thus, organoaluminium reagents can be used to desymmetrise sulfinylquinols by a diastereoselective conjugate addition to the enone fragment of the quinol 183 (Scheme 83). 151 A variety of alanes can be used and in all the cases described, only one single diastereoisomer is obtained. …”
Chiral sulfinyl groups have been widely used in organic synthesis as a stereo-and enantiodirecting functionality and the high efficiency of the selectivity has received much attention in recent years. In this review we wish to cover the work published in the literature since 1996. The participation of a chiral sulfinyl function in a wide range of reactions as well as the application of these methodologies to the synthesis of natural products are reported.
“…The authors proposed that this lack of diastereoselectivity was due to the electrophilic nature of the aluminum reagent compared to the nucleophilic nature of methyl Grignard or methyllithium organometallics. However, with methyl ether 30 , an 8:2 anti-selectivity was achieved at −78 °C, albeit in low yield, and substrate 15 provided a large preference for the anti -addition product 33 (Scheme ) 5 6 …”
Section: 2-additions Of Grignard and Organolithium
Reagents To 44-dis...mentioning
“…The reactions of 1 with organocuprates, which typically gave conjugate additions, yielded complex reaction mixtures. Only organoaluminum reagents , gave satisfactory results. The reactions of 1 with AlR 5 R 6 2 were carried out with an excess of the reagent (4 equiv) at low temperature (−78 or 0 °C) in CH 2 Cl 2 to afford only one product 10 (Table , entries 4, 7, and 9−11) out of the six possible isomers that could result from 1,2- or 1,4-addition.…”
Section: Resultsmentioning
confidence: 97%
“…Enantiomerically pure ( R )-4-hydroxy-4-[( p -tolylsulfinyl)methyl]-2,5-cyclohexadienones 1 − 3 (Table ) were prepared as previously described. ,6b The synthesis of asymmetrically substituted compounds 4 and 5 was achieved from p -quinol 1 in a two-pot, three-step sequence based on 1,4-addition of AlMe 3 or AlEt 3 and trapping the intermediate aluminum enolate with NBS followed by HBr elimination upon heating a DMF solution of bromo derivatives 7 and 8 with Li 2 CO 3 /LiBr (Scheme ). Inspection of the crude reaction mixture resulting after NBS treatment revealed that compounds 7 and 8 were stereoselectively formed as 5,6-trans diastereomers, but after chromatographic purification, a 1:1 mixture of cis and trans isomers was recovered.…”
(R)-4-Hydroxy-4-[(p-tolylsulfinyl)methyl]-2,5-cyclohexadienones
1−3, and 6 reacted with
organoaluminum derivatives from the pro-R conjugated position in a
highly π-facial diastereoselective manner
directed by the C-4 OH. A similar facial diastereoselectivity
arose from reactions with 3-alkyl-substituted analogues 4 and 5 and
5-alkyl-4-hydroxy-4-[(p-tolylsulfinyl)methyl]-2-cyclohexenones
10a,b. Semiempirical calculations (AM1 model) provide
data on transition-state energies for
additions in full agreement with the experimental results.
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