Chiral Allylsilane Additions to Chiral alpha-Substituted Aldehydes

Abstract

Re a ção do alil si la no qui ral 3 com α-me til-β-si lo xi-aldeídos for ne ce os pro du tos cor res ponden tes com es te re o quí mi ca re la ti va 1,4syn com boa di as te re os se le ti vi da de, in de pen den te da es te re o quí mi ca ab so lu ta dos al de í dos. As me lho res se le ti vi da des são ob ser va da s quan do ocorre trans me ta la ção do alil si la no 3 usan do SnCl 4 em CH 2Cl 2, a-78 °C, an tes da adi ção dos al de ídos. Chi ral allylsi la ne 3 re ac ted with chi ral α-methyl-β-si loxy-aldehydes to af ford the cor respon ding 1,4-syn-products with good di as te re o se lec ti vi ti es in de pen dent of the ab so lu te ste re oche mistry of the se al dehy des. The best se lec ti vi ti es are ob ser ved when the re ac ti ons are car ri ed out by trans me tal la ti on of the allylsi la ne 3 using Tin (IV) Chlo ri de in CH 2Cl 2, at-78 °C, be fo re ad di ti on of the al dehy des. Key words: chi ral allylsi la ne, trans me tal la ti on, 1,4-asymmetric in duc ti on, pol ya ce ta te de ri ved na tu ral pro ducts Ar ti cle Dedicated to Prof. José Tércio Barbosa Ferreira (in Memoriam) and to the Brazilian Chemical Society (SBQ)

Addition of chiral and achiral allyltrichlorostannanes to chiral±-alkoxy aldehydes

“…[3][4][5][6][7][8][9][10][11]14 According to previously established experimental procedures, the allylsilanes were mixed with SnCl 4 (1.0 equiv. in CH 2 Cl 2 ) before the addition of a solution of the aldehyde in order to promote the SiMe 3 /SnCl 3 exchange leading to the corresponding allyltrichlorostannanes 5-8 (Scheme 1).…”

“…13 In 1999, we described the first direct evidence for interaction between SnCl 4 and chiral allylic silane 3 bearing an ether functionality that generated a new species by means of NMR spectroscopy. 5 In a continuation of these initial studies we have done a spectroscopic study ( For allyltrimethylsilane 1 the SiMe 3 /SnCl 3 exchange producing allyltrichlorostannane 5 and Me 3 SiCl is complete after 2 h at room temperature (Scheme 1). 5 For allylsilane 2 the SiMe 3 /SnCl 3 exchange to give 6 and Me 3 SiCl is faster, as expected for a 1,1-disubstituted electron-rich olefin, being complete after 10 minutes at room temperature.…”

“…5 In a continuation of these initial studies we have done a spectroscopic study ( For allyltrimethylsilane 1 the SiMe 3 /SnCl 3 exchange producing allyltrichlorostannane 5 and Me 3 SiCl is complete after 2 h at room temperature (Scheme 1). 5 For allylsilane 2 the SiMe 3 /SnCl 3 exchange to give 6 and Me 3 SiCl is faster, as expected for a 1,1-disubstituted electron-rich olefin, being complete after 10 minutes at room temperature. 14 3 , at −60 o C, slightly yellow homogeneous solutions were obtained.…”

“…We recently communicated that in situ prepared chiral allyltrichlorostannanes react with chiral aldehydes to give 1,4-syn homoallylic alcohols with high levels of diastereoselectivity. [3][4][5][6][7][8][9][10][11] We wish to describe here a stereocontrolled reaction between achiral and chiral allyltrichlorostannanes with chiral lactate-derived aldehydes to give fragments which can be found in a large variety of naturally-occurring products with promising biological activities. 12 This study details our efforts to understand the double stereodifferentiating stereocontrol elements involved in chiral allyltrichlorostannane additions to chiral aldehydes.…”

“…Addition of achiral allyltrichlorostannanes 5 and 6 to aldehyde (S)-11 Previous work from our laboratory showed that allyltrichlorostannane (R)-7 reacted with achiral aldehydes leading to the formation of 1,4-syn products as the major isomers (up to > 95:5 diastereoselectivity). [3][4][5][6][7][8][9][10][11] At this point we initiated the double stereodifferentiating studies involving allyltrichlorostannane (R)-7 and chiral aldehydes 11 and 12. Addition of allyltrichlorostannane (R)-7 to aldehyde (S)-11 in CH 2 Cl 2 at −78 °C gave an 85:15 mixture of diastereoisomers 19 and 20, respectively, in 70% yield for the two-step sequence (Scheme 4).…”