Substrate-controlled formal synthesis of (+)-laurenyne by a chemoselective chelation-controlled alkylation strategy

Heterocycles

Volumn 74, Issue C, 2007, Pages 171-175

  Kim, Byungsook ^a   Cheon, Gukwha ^a   Park, Janghyun ^a   Lee, Hyunjoo ^a   Kim, Hyoungsu ^a   Kim, Sanghee ^a   Kim, Deukjoon ^a  

^a Seoul National University   (South Korea)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 40749092903     PISSN: 03855414     EISSN: None     Source Type: Journal    
DOI: 10.3987/com-07-s(w)41     Document Type: Article

References (18)

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8. 5 Unlike the case of S, the C(7) and C(8) substituents in cup-shaped bidentate enolate intermediates C and C are trans-oriented. Our ensuing studies revealed that the size of the R group at C(8) has a dramatic influence on the stereochemical outcome of alkylation as shown below. Thus, in the case of 5'a (R = Et) in which the C(7) and C(8) substituents are similar in size (allyl vs ethyl), the C(7) substituent seems to prefer to be disposed on the convex face, leading to the formation of cup-shaped bidentate intemediate C. Electrophilic attack from the convex β-face of the cup-shaped bidentate model C (described as electrophilic attack from the side opposite to the ethyl group in bidentate model in our original paper) would then produce the corresponding syn isomer. We substantiated this argument by introducing the identical allyl group at the C(8) position (5'b). However, we find that alkylation of 5'c (R = isopropyl) proceeds by electrophilic attack from the convex α-face of cup-shaped bidentate model C' to give the anti isomer exclusively since the branched bulky isopropyl group at C(8) prefers to be located on the less hindered convex face.
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