Model compounds MC1 and MC2 with three-and two-carbon spacers between sulfur and carbonyl moiety, respectively, were synthesized (Schemes 1b, S3; note: 4-nitrophenyl carbamate is more stable than 4-nitrophenyl carbonate, which allows monitoring of the degradation using NMR spectroscopy). When MC1 was subjected to Pd(0) in the presence of NMA and DBU, only the thiol intermediate was formed without generating reporter molecule 4-nitroaniline, even 7 days (Figure ). In contrast, MC2 showed complete degradation, generating 4-nitroaniline quantitatively after 24 h under identical conditions (Figure ). These results confirmed that the spacer length determines the propensity of cyclization and that the elimination-cyclization sequence proceeded efficiently for MC2. Cyclization presumably occurs much more rapidly with the two-carbon spacer due to the formation of the three-membered thiirane, in agreement with previous work (Scheme S10). Encouraged by these results, two additional model compounds MC3 and MC4 from lignin-derived vanillin and 4-hydroxybenzaldehyde, respectively, were prepared to probe the electronic effects on the elimination reactions (Schemes 1b, S4). The relative rates of liberation of 4-nitroaniline after Pd(0) triggering followed the order MC2>MC3>MC4 (Figures S30,S44,S46,S48), suggesting an acceleration effect from electrondonating methoxy substituents, which could be explained by more favorable dearomatization to facilitate the 1,6-elimination. Favorably, MC2 and MC1 with two methoxy substituents also exhibited the highest stability in the absence of Pd(0), which can be explained by the strong steric hindrance around the carbonate linkage (Figures S29,S31,S45,S47,S48).