Dibutyltin oxide mediated diastereoselective cyclodehydration/sulfonylation of 1,2,4-triols
摘要:
Dibutyltin oxide (Bu2SnO) mediated cyclodehydration or sulfonylation of 1,2,4-triols is predictably diastereoselective depending on the steric bulk of the substituents at C4. A larger difference (Delta A-value >1 kcal/mol) leads to the syn-1,2,4-triols favouring cyclodehydration (78-85%) to form 3-hydroxytetrahydrofurans, with the anti-1,2,4-triols favouring monosulfonylation (66-87%). Triols from symmetrical ketones preferentially undergo cyclodehydration in high yield (>75%) due to a gem-disubstituent effect. Thus, the 1,2,4-triols derived from simple cyclic ketones also favour cyclodehydration to form spirocyclic 3-hydroxytetrahydrofurans in 72-79% yields. (C) 2015 Elsevier Ltd. All rights reserved.
Dibutyltin oxide mediated diastereoselective cyclodehydration/sulfonylation of 1,2,4-triols
作者:Makhosazana P. Gamedze、Comfort M. Nkambule
DOI:10.1016/j.tetlet.2015.02.083
日期:2015.4
Dibutyltin oxide (Bu2SnO) mediated cyclodehydration or sulfonylation of 1,2,4-triols is predictably diastereoselective depending on the steric bulk of the substituents at C4. A larger difference (Delta A-value >1 kcal/mol) leads to the syn-1,2,4-triols favouring cyclodehydration (78-85%) to form 3-hydroxytetrahydrofurans, with the anti-1,2,4-triols favouring monosulfonylation (66-87%). Triols from symmetrical ketones preferentially undergo cyclodehydration in high yield (>75%) due to a gem-disubstituent effect. Thus, the 1,2,4-triols derived from simple cyclic ketones also favour cyclodehydration to form spirocyclic 3-hydroxytetrahydrofurans in 72-79% yields. (C) 2015 Elsevier Ltd. All rights reserved.
Formation of chiral tertiary homoallylic alcohols via Evans aldol reaction or enzymatic resolution and their influence on the Sharpless asymmetric dihydroxylation
作者:Matthias Theurer、Peter Fischer、Angelika Baro、Giang Son Nguyen、Robert Kourist、Uwe Bornscheuer、Sabine Laschat
DOI:10.1016/j.tet.2010.03.048
日期:2010.5
Enantioenriched tertiary homoallylic alcohol derivatives (S)-2c and (S)-2a were obtained via Evans aldol methodology and enzymatic resolution of racemic tertiary acetate 2e, respectively. In order to study asymmetric 1,3-induction of the stereogenic center present in 2, congener (R)-2a as well as its O-protected derivatives (R)-2b–d were submitted to Sharpless asymmetric dihydroxylation to yield the