Substrate scope of various alcohols 2 ^a.

^aReaction conditions: 4-nitrobenzaldehyde (1a, 3.0 mmol), alcohol 2 (1.0 mmol), VB1 (0.2 mmol), and DABCO (2.0 mmol) in acetone (2.0 mL) at 60 °C (oil bath) for 24 h under air; isolated yields.