Assignment of the relative configuration of spiro[4.5]decanes by ¹³C, ¹⁵N and ¹⁷O NMR

Abstract

The relative configuration of 11 1,4-diazaspiro[4.5]decanes (1a-1j and 1m), 15 1,4-oxazaspiro[4.5]decanes (2a-2o) and 10 1,4-dioxaspiro[4.5]decanes (3a-3n) substituted at the 2-, 6-, 7- or 8-position by a methyl group or using the tert-butyl group as a model for the ananchomeric structure is reported. The relative stereochemistry was analyzed by 1H, 13C, 15N and 17O NMR and all isomers present were characterized spectroscopically. Compounds with a methyl group in the six-membered ring show a chair conformation preference with the methyl group in the equatorial position. Compounds with one or two nitrogens exhibit a tautomeric equilibrium between the imine-diazolidine forms, as demonstrated by IR and 13C NMR.

Structural and conformational analysis of 1‐oxaspiro[2.5]octane and 1‐oxa‐2‐azaspiro[2.5]octane derivatives by 1H, 13C, and 15N NMR

“…Additionally, the syn‐anti isomer of compound 2c yielded a Δδ N of 2.4, similar to that observed for 4c (Δδ N = 2.3), whereas the difference was only 0.1 ppm for compound 3c . These observations agreed well with previously reported observations for spiro[4.5]decanes …”