Conformation diazocarbonyl compounds

This result is in excellent agreement with the alcohol-trapping experiments of Platz and co-workers [94], who isolated essentially only carbene-derived adducts and with the calculations of Zhu et al. [93], Those calculations indicate that diazoester 1 is planar and exists almost entirely (99%) in conformations in which the diazo and carbonyl groups are anti. Previously, Kaplan and co-workers [105] demonstrated that diazocarbonyl compounds can exist as equilibrium mixtures of syn and anti forms (e.g., 6sy and 6anti)- Kaplan s group, as well as Tomioka et al. [106] and Platz and co-workers [107], have shown that concerted rearrangement to ketene from an excited state is facile from the syn conformation, but carbene production is more likely from the anti form (Scheme 2.9) [108]. (Carbene formation can also occur from the syn form.) Thus, the preferred conformation of 6 leads to efficient carbene production upon photolysis with very little if any direct rearrangement to ketene 3. 

Several studies have indicated that the conformation of the diazo precursor plays a critical role in the pathway of the Wolff rearrangement. Kaplan and co-workers were the first to demonstrate that diazocarbonyl compounds exist as an equihbrium mixture of sy and anti forms and that concerted rearrangement... 

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