p-Hydroxyphenacyl is an effective photoremovable protecting group, not least due to the fast release of its substrates, accompanied by a photo-Favorskii rearrangement of compounds 1 to p-hydroxyphenylacetic acid (2) that is transparent down to 300 nm. First used for the release of ATP from 1 (X = ATP) a decade ago, 1 the reaction has been employed in a variety of fields as diverse as neurobiology, 2 enzyme catalysis, 3 and biochemistry. 4 The nature and timing of the bond-making and bond-breaking events have not been fully elucidated despite extensive experimental and theoretical efforts by our group 5 and others. 6,7 We now report observation of the primary photoproduct, the triplet biradical 3 3, and of a new side product, p-hydroxybenzyl alcohol (6), that is formed by decarbonylation of the putative spirodione intermediate 4 at moderate water concentrations (Scheme 1). Solvent kinetic isotope effect (SKIE) studies by nanosecond laser flash photolysis (LFP) provide significant information on the role of water in the photo-Favorskii rearrangement of p-hydroxyphenacyl diethyl phosphate 1a to p-hydroxyphenylacetic acid (2). Anderson and Reese first reported the intriguing photoreaction 1(X = Cl) → 2 + HCl and suggested that the skeletal rearrangement may proceed via a spirodione intermediate 4, 8 which has yet to be detected. Intersystem crossing (ISC) of diethyl phosphate 1a is very fast, k ISC = 4 × 10 11 s −1 , 5 and we have established that the rearrangement proceeds from the triplet state, T 1. 1,4b,5 This was confirmed by Phillips et al. 7a-c Hydroxylic solvents play a major role in the rearrangement. The lifetime of T 1 decreases from several μs in degassed, dry CH 3 CN to about 0.4 ns in aqueous CH 3 CN (50% by vol). 5,7c,d The lifetime of T 1 of 1a is further reduced to 100 ± 10 ps in 87% aqueous CH 3 CN (Figure 1) and to 63 ± 10 ps in wholly aqueous solution. This was the key to revealing that the decay of T 1 left weak absorptions at 445, 420, and 330 nm, which decayed with a somewhat longer lifetime of ca. 0.6 ns. Pump-probe spectra obtained with other derivatives of 1 with good leaving groups (1b,c: X = tosylate, mesylate) also displayed the transient species possessing

An abiotic formation of meso- and dl-tartrates in 80% yield via the cyanide-catalyzed dimerization of glyoxylate under alkaline conditions is demonstrated. A detailed mechanism for this conversion is proposed, supported by NMR evidence and 13C-labeled reactions. Simple dehydration of tartrates to oxaloacetate and an ensuing decarboxylation to form pyruvate are known processes that provide a ready feedstock for entry into the citric acid cycle. While glyoxylate and high hydroxide concentration are atypical in the prebiotic literature, there is evidence for natural, abiotic availability of each. It is proposed that this availability, coupled with the remarkable efficiency of tartrate production from glyoxylate, merits consideration of an alternative prebiotic pathway for providing constituents of the citric acid cycle.