ISSN:
0947-3440
Schlagwort(e):
Asymmetric induction
;
Diastereoselectivity
;
1,3-Diol
;
Lithiation, reductive
;
Rearrangement, retro-Brook
;
Silane, α-chiral
;
Silane, crotyl-
;
Silane, γ-hydroxy-
;
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Treatment of alcohols cis-22, cis-23, and trans-23 with PPh3/ Ph2S2 provided three mixtures of isomers of α, γ-disubstituted allyl phenyl sulfides. They consisted of diastereomers and -except starting from trans-23-of regioisomers. Each mixture was lithiated reductively by lithium naphthalenide at -78°C in THF. α, γ-Disubstituted allyllithium compounds resulted which underwent retro-[1,4]-Brook rearrangements within 30-90 min. A high degree of stereocontrol by 1,3-asymmetric induction was observed in the rearrangement starting from a 5:1 mixture of the tBuPh2Si-containing sulfide regioisomers cis-25 and iso-25 (each regioisomer consisting of more than one diastereomer): The α-chiral crotylsilane anti, trans-26 was formed as a racemic mixture with ds = 93:7:0:0 in preference to isomer syn,trans-26 which possesses the opposite configuration at the silicon-bearing stereocenter and in preference to the corresponding cis isomers (Scheme 5). The rearrangements of the two other sulfide mixtures were much less stereoselective and exhibited ds = 49:44:4:3 starting from the two tBuPh2Si-containing diastereomers of the isomeric sulfide trans-25 (Scheme 5) and ds = 59:41 starting from the 3.5:1 mixture of the MePh2Si-containing sulfide regioisomers cis-24 and iso-24 (each regioisomer consisting of more than one diastereomer; Scheme 9). The stereostructures of the rearrangement products were determined by chemical correlations, NMR analogies, and a crystal structure analysis of 27. It was proven that the stereochemical outcome of the retro-[1,4]-Brook rearrangements of the MePh2Si-containing 3.5:1 mixture of sulfides cis-24/iso-24 is kinetically rather than thermodynamically controlled (Scheme 10). Mechanistic aspects are discussed in Schemes 11-13.
Zusätzliches Material:
1 Tab.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jlac.199519950247
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