Letter Cite This: Org. Lett. 2018, 20, 6979−6983
pubs.acs.org/OrgLett
Catalytic [3 + 3]-Cycloaddition for Regioselective Preparation of Tricyclic Oxadiazines T. Prabhakar Reddy, A. Vamshi Krishna, and Dhevalapally B. Ramachary* Catalysis Laboratory, School of Chemistry, University of Hyderabad, Hyderabad-500 046, India
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S Supporting Information *
ABSTRACT: Agrochemically useful and structurally important, functionally rich tricyclic-oxadiazines were synthesized in very good yields with excellent diastereoselectivities through a catalytic [3 + 3]-cycloaddition from the readily available p-quinols, azomethine imines, and a catalytic amount of Brønsted base (KOtBu).
D
espite their simplicity, p-quinols (4-alkyl-4-hydroxy-2,5cyclohexadienones) and their derivatives have vast potential as significant building blocks in the synthesis of natural products such as cleroindicins C, D, and F, (−)-mesembrine, and clerobungin A as well as in reaction engineering, as is evident from past literature (Scheme 1).1,2 Owing to their versatile
aminal through a hemiaminalization step as shown in Scheme 1. At the same time, it is fascinating to study the [3 + 3]cycloaddition of p-quinols with 1,3-dipoles of azomethine imines to construct six-membered heterocyclic rings.5 Thus, this reaction design would furnish tricyclic-oxadiazine entity, which is not only fascinating but also functional. For instance, indoxacarb, an oxadiazine pesticide, acts against lepidopteran larvae and is the active ingredient in a number of household insecticides (Figure 1).6
Scheme 1. Reaction Design for the Tricyclic-Oxadiazines
Figure 1. Representative bioactive tricyclic-oxadiazines.
We initiated our study using p-quinol 1a and azomethine imine 2a as the starting materials and conducted the reaction in the presence of 20 mol % DBU 3a as catalyst in DCE at 25 °C for 24 h. Even though we observed the formation of the expected product tricyclic-oxadiazine 4aa, it was disappointing as the yield was very low (
