Structural studies of organoboron compounds. XLV. 5,5-Difluoro-2,2-pentamethylene-7,7-diphenyl-1,4,6-trioxa-3a-azonia-5-borata-2,3,4,5,6,7-hexahydroindene

Abstract

. Can. J. Chem. 69, 681 (1991).The reaction of N,2-dihydroxy-N-(1 -hydroxycyclohexyl)methyl-2,2-diphenylacetamide with dimethyl ether-boron trifluoride gives 5,5-difluoro-2,2-pentamethylene-7,7-diphenyl-,4,6-trioxa-3a-azonia-5-borata-2,3,4,5,6,7-hexahydroindene in nearly quantitative yield. Crystals of the product are triclinic, a = 9.4555(5), b = 9.9813(6), c = 10.5139(9) A, a = 72.654(7), P = 77.140(5), y = 88.542(6)", Z = 2, space group p i . The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.044 and R,,. = 0.060 for 2971 reflections with I 2 3u(I). The molecule has a six-membered difluoroboron chelate structure, confirming that the regioselective alkylation of N-substituted hydroxamic acids under non-basic conditions leads to imidate N-oxides in cases where intramolecular alkylation occurs. Bond lengths (corrected for libration): (3) Mots clis : compos&s organoborks, structure cristalline, compost bore.[Traduit par la redaction] Introduction The reaction of the bis(hydroxyalky1) substituted hydroxamic acid 1 with boron trifluoride did not lead to the difluoroboron chelate 2 having the "normal" BF2 hydroxamate structure that usually results from reactions of N-alkylhydroxamic acids with boron trifluoride (I), and which has been established by an X-ray crystallographic study of the simple prototype 3 (2). The crystalline compound obtained from the reaction of 1 with BF3-0Me2 produced spectra and elemental analyses showing not only HF elimination but also loss of H20. Neither infrared bands for 0-H stretching vibrations nor OH-proton signals in the 'H nmr spectra, both of which would arise from the hydroxyl groups of 2, were observed. These data suggest an intra-or intermolecular condensation of 1 and difluoroboron chelate formation leading to structures such as 4-7.A possible intermediate 2 could form the cyclic ether 4 by intramolecular condensation and still feature the five-membered BF2 hydroxamate chelate, similar to the cyclic ether compound

Structural studies of organoboron compounds L. 4-(2-Hydroxy-2,2-diphenylacetyl)- 6,6-pentamethylene-2-phenyl-1,3-dioxa-4-aza-2-boracyclohexane and 4-[2,2-difluoro-5,5-bis(4-methoxyphenyl)-1,3-dioxa-2-borata-4-cyclopentylidene]- 6,6-pentamethylene-2-phenyl-1,3-dioxa-4-azonia-2-boracyclohexane

“…The structure of 2 has been established by an X-ray crystallographic analysis (8). To assess the capability of the polyfunctional ligand 1 for similar reactions with organoboron compounds we reacted it with phenylboronic acid, which, like BF,, is both a Lewis acid and bears suitable leaving groups (the hydroxyl residues).…”

“…Borate complexes of this kind also play a role in drug synthesis via hydroxamates or in the blocking of hydroxamic enzyme inhibitors (6). Structures deviating from the "normal" type of hydroxamate complexes have been established for the reaction products of some polyfunctional hydroxamic acids with boron compounds (7,8).The reaction of the bis(hydroxyalky1)-substituted hydroxamic acid 1 with BF, leads to the formation of the difluoroboron chelate 2 via intramolecular ring closure to an oxazoline-N-oxide and the subsequent3 formation of the BF, chelate. The structure of 2 has been established by an X-ray crystallographic analysis (8).…”

“…Borate complexes of this kind also play a role in drug synthesis via hydroxamates or in the blocking of hydroxamic enzyme inhibitors (6). Structures deviating from the "normal" type of hydroxamate complexes have been established for the reaction products of some polyfunctional hydroxamic acids with boron compounds (7,8).…”