Preparation and X-ray Crystal Study of Benziodoxaborole Derivatives: New Hypervalent Iodine Heterocycles

Abstract

A series of heterocyclic compounds containing trivalent iodine, oxygen, and boron in a five-membered ring were prepared and structurally investigated by X-ray crystallography. 1-Chloro-4-fluoro-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol was synthesized by chlorination of 2-fluoro-6-iodophenylboronic acid followed by treatment of the intermediate iododichloride with water. 1-Acetoxy-4-fluoro-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol, 1-acetoxy-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol, and similar 1-substituted trifluoroacetate derivatives of benziodoxaborole were prepared the hypochlorite oxidation of 2-fluoro-6-iodophenylboronic acid or 2-iodophenylboronic acid in acetic or trifluoroacetic acid, respectively. 1-Acetoxy substituted benziodoxaborole can be further converted to the respective trifluoroacetate by treatment with trifluoroacetic acid or to the 1-hydroxy derivative by basic hydrolysis with aqueous NaHCO(3). X-ray structural studies of 1-chloro- and 1-trifluoroacetoxy substituted benziodoxaboroles 13, 17, and 18 have shown the presence of a planar five-membered heterocyclic ring with unusually short endocyclic I-O bond distance of 2.04-2.09 Å. Slow crystallization of 4-fluoro-1-trifluoroacetoxy-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol-3-ol from methanol resulted in the formation of a tetrameric macrocyclic structure 21 resulting from self-assembly of the initially formed 4-fluoro-1,3-dimethoxy-1H-1λ(3)-benzo[d][1,2,3]iodoxoborol. Structural parameters of the five-membered iodoxoborol ring, such as the planar geometry and the short B-O and O-I bonds lengths in 13, 17, and 18 compared to those in 21 and known benziodoxoles are indicative of partially aromatic character of this ring. Density functional theory (DFT) predicted NIST (0) and NIST (1) indexes for 1-chloro- and 1-trifluoroacetoxy substituted benziodoxaboroles, however, are indicative of significantly lower aromaticity compared to the classic aromatic systems.

Pseudocyclic Arylbenziodoxaboroles: Efficient Benzyne Precursors Triggered by Water at Room Temperature

“…Our approach to the synthesis of pseudocyclic arylbenziodoxaborole triflates is based on the ligand exchange reaction between the corresponding hypervalent iodine heterocycles (1‐acetoxybenziodoxaboroles) and arenes in the presence of strong acid . In the initial experiment, the reaction of 1‐acetoxy‐4‐fluorobenziodoxaborole 4 a (1 equiv) with mesitylene in the presence of triflic acid (2 equiv) under mild conditions afforded the corresponding 1‐mesitylbenziodoxaborole triflate 5 a in 95 % yield (Scheme ). Decreasing the amount of TfOH to 1.2 or 1.5 equiv resulted in a lower yield of the product 5 a .…”

Heterocyclic Hypervalent Iodine(III) Compounds with Fused Benziodazole and Tetrazole Rings (I-Substituted Tetrazolo[1,5-b][1,2]Benziodazoles)

“…11,20,47 In general, benziodoxoles have a planar structure with distorted T-shaped geometry around the HV iodine atom. More recent examples of I-O heterocyclic compounds include benziodoxaboroles, 48 benziodoxathioles, 49,50 and cyclic phosphonates. 51 In 1965, Wolf and Steinberg reported another class of heterocyclic HV iodine(III) compounds, the benziodazoles, in which the I(III) atom is bonded to a nitrogen atom in a five-membered ring fused to a benzene ring.…”

Preparation, structure, and reactivity of bicyclic benziodazole: a new hypervalent iodine heterocycle

“…Numerous examples of five-membered hypervalent iodine(III) heterocycles containing other than oxygen heteroatoms, such as sulfur [ 26 ], boron [ 27 – 28 ], phosphorous [ 29 ], or nitrogen [ 30 – 32 ], have been synthesized and characterized by X-ray crystallography. In particular, several nitrogen containing heterocyclic iodine(III) compounds 5 , benziodazoles, have been reported by Gougoutas [ 31 ], Balthazor [ 32 ], and our group [ 33 – 35 ] ( Scheme 1 ).…”