The propensity of a stable N,N′‐diamidocarbene (DAC) to react with various heteroallenes was explored. The DAC condensed with 4‐nitrophenyl azide as well as 4‐nitrophenyl isothiocyanate to afford the respective acyclic triazene or zwitterionic dihydropyrimidinium imidothiolate products. Treating the DAC with two equivalents of 3‐nitrophenyl isocyanate afforded an iminooxazolidinone rather than the expected hydantoin. Similarly, the addition of diphenylketene to the DAC afforded a dioxolane product, whereas analogous reactions involving N‐heterocyclic carbenes (NHCs) resulted in betaine adducts. Although the DAC as well as various diaminocarbenes condensed with 2,6‐dimethoxyphenyl nitrile N‐oxide to afford the respective nitrosoethylenes, only the six‐membered DAC and NHC adducts rearranged to the corresponding nitrones at elevated temperature. Copyright © 2012 John Wiley & Sons, Ltd.

S Supporting Information ■ INTRODUCTIONPolycyclic polymers continue to attract interest as high performance materials on account of their high degrees of chemical and thermal stabilities. 1,2 In particular, spiro-and other ladder-like polymers comprised of bicyclic repeat units wherein the rings connect through a common atom have received increasing attention due to their restricted rotational freedom and utility in forming thermally robust materials. 3,4 In some cases (e.g., the poly(spirobifluorene)s), the polycycles have been shown to adopt twisted helical structures that effectively prevented aggregation and enhanced their optical properties. 5−12 Unfortunately, the synthesis of spiro-polycycles is challenging due to the need for an efficient polymerization reaction that forms cyclic linkages between the repeating units. 12 Toward this end, we recently demonstrated that readily available N,N′-diamidocarbenes (DACs) 13−15 rapidly and selectively afford 2-imino-4-oxazolidinones 16 upon exposure to 2 equiv of an isocyanate. The reactivity was remarkable as most NHCs catalyze the cyclotrimerization of isocyanates to isocyanurates rather than undergoing cycloaddition chemistry. 17 We envisioned condensing DACs with bifunctional isocyanates to access new classes of polycycles with functionally rich heterocyclic cores. Herein we report the synthesis and study of novel polyspiro(iminooxazolidinone)s via the formal [2 + 2 + 1] cycloaddition of a stable DAC with various diisocyanates. The chemistry presented herein overcomes many of the challenges associated with the synthesis of stable spirocenters in polymeric materials and provides a unique approach to rapidly access a new structural class of polyheterocycles. ■ RESULTS AND DISCUSSIONPreviously, we demonstrated that an oxazolidinone forms upon treatment of DAC 1 with two equivalents of 3-nitrophenylisocyanate. In order to use this chemistry to form high molecular weight polymers, we anticipated that less polarized and more solubilizing diisocyanates, such as methylene diphenyl diisocyanate (MDI), would be advantageous. Thus, initial experiments focused on probing the reactivity and product selectivity of 1 with phenylisocyanate, a nonpolymerizable model. As summarized in Scheme 1, adding two equivalents of phenylisocyanate to a solution of 1 in benzene resulted in the initial formation of a purple solution that became colorless after stirring for an additional 1 h at room temperature. The product of this reaction (2) was subsequently isolated in high yield (98%) as a white solid by recrystallization from benzene/pentane. Characterization using 1 H and 13 C NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis supported the formation of a 2:1 isocyanate/DAC adduct. The structure of this product was unambiguously elucidated using single crystal X-ray diffraction (XRD) analysis (Figure 1, left), which confirmed the formation of the oxazolidinone heterocycle 2, rather than the isomeric hydantoin 3. 16 We postulated that the formation of 2 originate...