Regio- and stereoselectivities in Diels–Alder cyclodimerizations of orthoquinonoid cyclohexa-2,4-dienones
摘要:
The [4+2] cyclodimerization of cyclohexa-2,4-dienone derivatives of the orthoquinone monoketal and orthoquinol types has been the topic of numerous investigations over the last 50 years in the aim of rationalizing the extraordinary level of regio-, site-, and stereoselectivities observed in these processes. In particular, the double diastereo-pi-facial differentiation expressed in cyclodimerizations of chiral orthoquinols (i.e., 6-alkyl-6-hydroxycyclohexa-2,4-dienones) is an important aspect of these transformations, for they relate to the construction of several natural products. The experimental and theoretical results that are described in this article offer a comprehensive understanding of the factors controlling these site- specific regio- and diastereoselectivities. Our interpretation of these results relies on a combination of Wood-ward-Hoffmann and Salem-Houk secondary orbital interactions and Cieplak-type hyperconjugative effects in bispericyclic C-2-symmetric transition states. (c) 2007 Elsevier Ltd. All rights reserved.
′I′ is all the hype: A twofold excess of iodoarene in the title reaction leads to ortho‐quinols in good yields, whereas organocatalytic versions of this reaction enable subsequent epoxidation in a regio‐ and diastereoselective fashion. Chiral iodobiarenes led to enantioselectivities up to 50 % ee. m‐CPBA=meta‐chloroperoxybenzoic acid.
Asymmetric Hydroxylative Phenol Dearomatization Promoted by Chiral Binaphthylic and Biphenylic Iodanes
作者:Cyril Bosset、Romain Coffinier、Philippe A. Peixoto、Mourad El Assal、Karinne Miqueu、Jean-Marc Sotiropoulos、Laurent Pouységu、Stéphane Quideau
DOI:10.1002/anie.201403571
日期:2014.9.8
The long‐standing quest for chiral hypervalent organoiodine compounds (i.e., iodanes) as metal‐free reagents for asymmetric synthesis continues. Although remarkable progress has recently been made in organoiodine‐catalyzed reactions using a terminal oxidant in stoichiometric amounts, there is still a significant need for “flaskable” chiral iodane reagents. Herein, we describe the synthesis of new iodobinaphthyls
efficiently mediates the hydroxylative dearomatization of various 2-alkylphenols and napthols into orthoquinols or their [4 + 2] cyclodimers. Reactions are typically run at room temperature using SIBX as a suspension in THF. Using these conditions, natural products such as the cyclodimer of the terpene carvacrol and, for the first time, the shikimate-derived (±)-grandifloracin were prepared in one step from
dearomatization of 2‐substituted phenols to either 1,2‐benzoquinols or their cyclodimers, catalyzed by 4,5‐dimethyl‐2‐iodoxybenzenesulfonic acid with Oxone, has been developed. Natural products such as biscarvacrol and lacinilene C methylether could be synthesized efficiently under mild reaction conditions. Furthermore, both the reaction rate and site selectivity could be further improved by the introduction of
Amino acid-derived novel chiral hypervalent iodine(V) reagents were synthesized from the corresponding chiral iodoarenes through DMDO oxidations. Their oxidation states were determined by the 13C NMR chemical shifts of the ipso-carbon of the iodine atom, HRMS analysis, and elemental analyses. They were applied to the enantioselective hydroxylative dearomatization/[4+2]-dimerization cascade reactions
从相应的手性碘芳烃通过DMDO氧化合成了氨基酸衍生的新型手性高价碘试剂。它们的氧化态由碘原子的ipso-碳的13 C NMR化学位移,HRMS分析和元素分析确定。将它们用于苯酚衍生物的对映选择性羟基化脱芳香化/ [4 + 2]-二聚级联反应,得到所需产物,其ee最高为58%。