Stereoselective Conjugate Addition of Benzyl Phenylsulfonyl Carbanions to Enoates Derived from d-Mannitol

The conjugate addition of benzylic phenylsulfonyl carbanions (2a‘− d‘) to enoates derived from d-(+)-mannitol (E- or Z-1a − c) was studied using THF and THF/HMPA as solvent. Under kinetic conditions (−78 °C), enoate E-1a,b led to a mixture of syn-(R,S) and anti-(S,S) adducts (55/45), and syn-(R,S) a...

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Bibliographic Details
Published in:	Journal of organic chemistry Vol. 69; no. 12; pp. 4013 - 4018
Main Authors:	Ferreira, André R. G, de A. Vilela, Guilherme V. M, Amorim, Mauro B, Perry, Kátia P, da Silva, Antônio J. R, Dias, Ayres G, Costa, Paulo R. R
Format:	Journal Article
Language:	English
Published:	Washington, DC American Chemical Society 11-06-2004
Subjects:	Chemistry Exact sciences and technology Heterocyclic compounds Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives Kinetics and mechanisms Organic chemistry Preparations and properties Reactivity and mechanisms Configuration Sulfone Ab initio method Chiral compound NMR spectrometry Carbanion Syn stereoisomer Oxygen heterocycle Tetrahydrofurane Hydrogen 1 Chemical reduction Stereoselectivity Ester Thermodynamics Benzylic compound Mannitol Reaction mechanism Chemical synthesis Acid medium Moller Plesset partition Theoretical study Hexamethylphosphorotriamide Lactone Addition reaction Kinetics Aqueous solution Conformational equilibrium Ethylenic compound Sodium Mercury
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Summary:	The conjugate addition of benzylic phenylsulfonyl carbanions (2a‘− d‘) to enoates derived from d-(+)-mannitol (E- or Z-1a − c) was studied using THF and THF/HMPA as solvent. Under kinetic conditions (−78 °C), enoate E-1a,b led to a mixture of syn-(R,S) and anti-(S,S) adducts (55/45), and syn-(R,S) adducts were the main product obtained (∼90/10) from enoate Z-1a. Under thermodynamic conditions (−78 °C to room temperature) syn-(R,S) adducts were also preferentially formed (∼90/10), despite the geometry at the double bond in the acceptor. Enoate 1c (E/Z = 57/43), bearing an additional benzyl group at the α-position, also reacted with carbanions 2‘a,b, under thermodynamic conditions, leading to syn-adducts in excellent de (control at the three newly generated stereogenic centers). The adducts were quantitatively transformed into the corresponding β-γ-disubstituted γ-butyrolactones and α,β,γ-trisubstituted γ-butyrolactones. 1H NMR studies (NOE and J-coupling) of these lactones allowed us to determine their configuration at the newly generated chiral centers. The reduction of the C−S bond in adducts syn-(R,S) with Na/Hg, followed by treatment of the resulting products in aqueous acid media, led to enantioenriched β-benzyl-γ-hydroxymethyl-γ-butyrolactones. The conformational equilibrium of enoates E- and Z-1b was evaluated by theoretical calculations (ab initio, MP2/6-31G*), and a mechanistic rationale was proposed to explain the observed stereoselectivities.
Bibliography:	ark:/67375/TPS-M5NC8HVS-D istex:50F2E0E9F4DE0C5368FE51A431A4C23C69932281 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0022-3263 1520-6904
DOI:	10.1021/jo035427d