Note Cite This: J. Org. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/joc
Transition-Metal-Free Benzannulation of Tricarbonyl Derivatives with Arynes: Access to 1,3-Dinaphthol Precursors for the Synthesis of Rhodamine Dye Analogues Ganesh S. Ghotekar,†,‡ Aslam C. Shaikh,† and M. Muthukrishnan*,†,‡ †
Division of Organic Chemistry, CSIR-National Chemical Laboratory, Pune 411008, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
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‡
S Supporting Information *
ABSTRACT: Herein, we report a transition-metal-free annulation reaction of benzynes and 1,3-oxopentanedioate for the synthesis of highly functionalized naphthalene derivatives for the first time. Additionally, the representative naphthalene derivatives have been successfully transformed into the new series of rhodamine dye analogues.
T
agents,4 serotonin 5-HT1A inhibitors, etc.5 Despite the multifunctional utility of this core, however, approaches for its synthesis are very limited, and often they are laborious, multistep processes and require the use of metals.6 Therefore, the development of novel and efficient one-step strategy to access these kinds of valuable intermediates from readily available starting material is ideal and highly desirable.7 Over the past few decades, transition-metal-free organic transformations have received a great deal of attention over the conventional synthetic methods, allowing the expeditious and sustainable formation of diverse chemical scaffolds.8 Nevertheless, the design and development of novel benzannulated analogues via aryne-based chemistry,9 especially in the absence of transition metals has tremendous potential. Recently, various types of aryne annulation strategy have been developed under metal-catalyzed or metal-free conditions because they facilitate the π-extension in a single step, and the final products are very important in terms of synthetic and applications perspectives.10 In particular, the [2+2+2] cycloaddition reaction is one of the appropriate and useful strategies for the construction of a naphthalene core.11 Such as, Xie and Yamamoto et al. described the synthesis of substituted naphthalene derivatives employing nickel- and palladiumcatalyzed coupling reactions between aryne−alkyne−alkene, respectively.12 In addition, the aryne−alkyne−alkyne cocyclization reaction catalyzed by palladium also gives access to a variety of polysubstituted naphthalene rings.13 Further, Huang and co-workers reported the synthesis of polysubstituted
he synthesis of functionalized polycyclic aromatic compounds has always been of immense interest to organic chemists, owing to their wide utility in organic, medicinal, and material applications.1 Among these, functionalized naphthalenes of type A are important fluorophores2 and are valuable intermediates in the synthesis of complex target molecules such as Nile red dyes, rhodamine dyes, and azodyes, and also, they are involved in the synthesis of several amide linkers that are required in the solid-phase synthesis (Figure 1).3 In addition, they are an important starting material for the preparation of medicinally important hypoglycemic
Figure 1. Representative examples showing the utility of a functionalized naphthalene core of type A. © XXXX American Chemical Society
Received: October 4, 2018 Published: January 10, 2019 A
DOI: 10.1021/acs.joc.8b02560 J. Org. Chem. XXXX, XXX, XXX−XXX
Note
The Journal of Organic Chemistry Table 1. Optimization of Reaction Conditionsa,b
naphthols and naphthalenes using a multicomponent reaction between arynes, β-keto sulfones, and Michael-type acceptors.14 In 2016, Wu and co-workers reported the synthesis of polyfunctional naphthalene derivatives using an aryne− alkyne−ketone coupling annulation reaction.15 Treatment of arynes with diketo compounds is found to be the alternate strategy to construct the naphthalene system. With this strategy, the research group of Stoltz and co-workers reported the synthesis of naphthoquinones via a one-pot aryne acylalkylation/condensation employing arynes with diketo compounds (Scheme 1, eq 1).16 In 2012, Okuma et al. reported an Scheme 1. Synthesis of Polycyclic Compounds Employing Arynes and Di/Tricarbonyl Compounds: Previous Work and This Work
entry
base
solvent
temp (°C)
yield (%)b
1 2 3 4 5 6 7 8 9 10 11
CsF CsF CsF CsF CsF CsF KF TBAF CsF CsF
CH3CN CH3CN CH3CN THF CHCl3 toluene CH3CN CH3CN CH3CN CH3CN CH3CN
rt 50 80 80 80 80 80 80 80 80 80
18 28 71
