Abstract
The selective synthesis of 2,6-trans-tetrahydropyran derivatives employing the rhodium catalysed addition of organoboron reagents to dihydropyranone templates, derived from a zinc-catalysed hetero-Diels-Alder reaction, is reported. The addition of both arylboronic acids and potassium alkenyltrifluoroborates have been accomplished in high yields using commercially-available [Rh(cod)(OH)]2 catalyst. The selective formation of the 2,6-trans-tetrahydropyran stereoisomer is consistent with a mechanism involving alkene association and carbometalation on the less hindered face of the dihydropyranone.
Highlights
The rhodium-catalysed conjugate addition of organometallic donors has evolved into a versatile tool for the assembly of complex molecules and intermediates in natural product synthesis [1,2,3,4,5,6]
We describe a general selective synthesis of 2,6-trans-tetrahydropyran derivatives employing the rhodium-catalysed addition of organoboron reagents to dihydropyranone templates derived from a HDA reaction
The selective formation of the 2,6-trans-tetrahydropyran stereoisomer is consistent with a mechanism involving alkene association and carbometalation on the less hindered face of the dihydropyranone, which affords the 2,6-trans-tetrahydropyran derivative on protonation of the rhodium oxa-π-allyl species (Figure 2)
Summary
The rhodium-catalysed conjugate addition of organometallic donors has evolved into a versatile tool for the assembly of complex molecules and intermediates in natural product synthesis [1,2,3,4,5,6]. Tetrahydropyran (THP) rings are a prevalent feature in natural products and such compounds frequently have important biological activities (Figure 1). In this context, the selective assembly of the 2,6-trans-tetrahydropyran subunit is a significant challenge [14]. A powerful methodology for the construction of 6-membered heterocycles is the hetero-Diels-Alder (HDA) cycloaddition [15]. This has been a key reaction for the synthesis of many THP containing natural products [16,17]. We describe a general selective synthesis of 2,6-trans-tetrahydropyran derivatives employing the rhodium-catalysed addition of organoboron reagents to dihydropyranone templates derived from a HDA reaction
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