Recent advances in transition-metal-free conversion of aldehydes to ketones

The preparation of functionalized ketones occupies an important position in synthetic organic chemistry because ketones are ubiquitous structural motifs in a broad range of compounds with various applications. The conversion of aldehydes to ketones is one of the most convenient and straightforward routes, which has been extensively studied in the field of transition metal catalysis. In comparison, the transition-metal-free conversion of aldehydes to ketones remains underdeveloped. In the last decade, the emergence of new advances has upgraded the toolbox for ketone synthesis from aldehydes in the absence of transition metals. In this review, we have mainly summarized three types of transition-metal-free reactions enabling the conversion of aldehydes to ketones, with an emphasis on those involving main group element catalysis.