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Download fileBidirectional Asymmetric Allylboration. A Convenient Asymmetric Synthesis of C2-Symmetric 3-Methylenepentane-1,5-diols and Rapid Access to C2-Symmetric Spiroketals
journal contribution
posted on 1999-12-29, 00:00 authored by Anthony G. M. Barrett, D. Christopher Braddock, Pieter D. de Koning, Andrew J. P. White, David J. WilliamsThe double allylboration of aldehydes using 1,3-bis(diisopinocampheylboryl)-2-methylenepropanes
(R,R)-3 and (S,S)-3 under Brown's salt-free conditions provides C2-symmetric 3-methylenepentane-1,5-diols 1 in excellent enantiomeric excess. The absolute stereochemistry of the products was
confirmed by a single-crystal X-ray study of bis-Mosher ester 6g. Desymmetrization and further
functionalization of diol 1a were achieved by treatment of the bis-BOC carbonate 13 with IBr in
toluene at −80 °C to give cyclic iodocarbonate 14 as a single diastereomer. This methodology is
also applicable in natural product synthesis; enantiomerically pure spiroketals 1,7-dioxaspiro[5.5]undecanes 18 and 25, the latter representing an expedient synthesis of the AB ring system of the
spongistatins 20, were easily accessed from simple starting materials in excellent yields and
selectivities.
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selectivitieAccessRapidcyclic iodocarbonate 14allylborationConvenient Asymmetric SynthesisspongistatinmaterialdiastereomertoluenedioxaspiroyieldDesymmetrizationSymmetricenantiomericallyspiroketalbiSpiroketalBidirectional Asymmetric AllylborationAB ring systemsynthesisesterdiolmethylenepentaneC 2lattermethodologyaldehydefunctionalizationstereochemistryIBrMethylenepentaneenantiomeric