Six-membered cyclic amines (piperidines, piperazines and morpholines) abound in bioactive compounds. By contrast, seven-membered cyclic amines are far less common, and their incorporation into 6,7-spirocycles, is even more unusual. We therefore sought to extend our methodology to the 6,7-spirocyclic homologue of 6,6-spiroacetal 9, which would represent a novel scaffold for compound library assembly. Iodoacetalization of enol ether 2f using N-Boc-propanolamine proceeded uneventfully to provide the corresponding iodide. a Average isolated yields after HPLC purification, isolated yields for each library product are included in the Supporting Information. Subsequent formation of the 1,4-oxazepane using our established cyclization conditions proved inefficient; the slow reaction led to competing formation of a urea by-product 19 (Scheme 4). The base-mediated elimination of t-BuOH from Boc carbamates to afford an isocyanate has been reported. We postulate urea 19 arises from isocyanate trapping with dimethylamine, which originates from the slow decomposition of the DMF solvent under the reaction conditions. While the use of different bases (K2CO3, Cs2CO3, Ag2CO3, NaH), solvents (THF, MeCN) and reaction temperatures (rt-90 ˚C) led to no improvement, we eventually found that urea formation was suppressed by performing the reaction in DMF solvent at higher concentration (0.2 M) and using 2 equiv. of t-BuOK; the increased rate of cyclization allowed isolation of oxazepane 20 in 70% yield. Exchanging the benzyl protecting group in 20 for a Cbz carbamate provided orthogonally protected 6,7-spiroacetal scaffold 21 in high yield. Efforts to synthesize the corresponding 6,8-and 6,9-spiroacetals failed (see the Supporting Information).