Accumulating evidence indicates that some ultraluminous X-ray sources (ULXs) are intermediate-mass black holes (IMBHs), but the formation process of IMBHs is unknown. One possibility is that they were formed as remnants of Population III (Pop. III) stars, but it has been thought that the probability of being a ULX is too low for IMBHs distributed in galactic halos to account for the observed number of ULXs. Here we show that the number of ULXs can be explained by such halo IMBHs passing through a dense molecular cloud if Pop. III star formation is very efficient as recently suggested by the excess of the cosmic near-infrared background radiation that cannot be accounted for by normal galaxy populations. We calculate the luminosity function of X-ray sources in our scenario and find that it is consistent with observed data. Our scenario can explain the fact that ULXs are preferentially found at the outskirts of large gas concentrations in star-forming regions. A few important physical effects are pointed out and discussed, including gas dynamical friction, radiative efficiency of the accretion flow, and radiative feedback to the ambient medium. ULXs could last for $10 5 -10 6 yr to emit a total energy of $10 53 ergs, which is sufficient to power the ionized expanding nebulae found by optical observations.

A direct asymmetric benzoyloxylation of aldehydes with benzoyl peroxide was found to be catalyzed by (S)-2-(triarylmethyl)pyrrolidines (S)-2. This method provides a new approach for the preparation of optically active alpha-benzoyloxyaldehydes as useful chiral building blocks.

Chiral a-hydroxy carbonyl motifs are prevalent in natural products and biologically active compounds, and are versatile building blocks for the synthesis of structurally complex molecules. It is known that such chiral a-hydroxy carbonyl compounds are prepared by asymmetric oxygenations of preformed enolates and enamines, such as epoxidation, [1] dihydroxylation, [2] and aminoxylation. [3] Over the past several years, a number of direct asymmetric a-oxygenations of aldehydes and ketones catalyzed by chiral secondary amines have been reported. [4][5][6][7][8] In this area, nitroso compounds have been commonly utilized as an electrophile for asymmetric aaminoxylation, and virtually optically pure a-aminoxy carbonyl compounds have been prepared. However, the aaminoxy aldehydes and the reduced b-aminoxy alcohols produced are highly labile, probably owing to oligomerization and/or NÀO bond cleavage. [4] Recently, Sibi and Hasegawa reported the asymmetric aaminoxylation of aldehydes using a stable radical, 2,2,6,6-tetramethylpiperidine 1-oxyl free radical (TEMPO), [5] which is considered to progress via a radical coupling pathway between TEMPO and the enamine radical cation generated from the enamine intermediate and a metal single electron oxidant (Scheme 1 a).[9-11] Whilst this metal-promoted reaction requires further improvement of the reaction conditions and the substrate scope, the resulting aminoxy aldehydes are attractive chiral building blocks as O-protected a-hydroxy aldehydes because of their stability. Accordingly, we have been interested in the possibility of utilizing oxoammonium salt 1, which could be generated in situ by oxidation from TEMPO, as a non-metal single-electron oxidant and an aminoxylating agent in the aminoxylation of aldehydes (Scheme 1 b). Herein, we report a metal-free organocatalytic asymmetric aminoxylation of aldehydes using TEMPO and benzoyl peroxide (BPO) with high enantioselectivity and broad substrate scope.To oxidize TEMPO into 1, which is known as a catalyst in TEMPO oxidation, [12] BPO was chosen as an organic oxidant. In the presence of chiral pyrrolidine catalyst (S)-2, [8a] 3-phenylpropanal was first treated with TEMPO and BPO in dichloromethane at 0 8C. As expected, the reaction proceeded to give the desired a-aminoxy aldehyde. To determine the enantioselectivity of the reaction, the product was reduced in situ with NaBH 4 to the corresponding alcohol 6, and the enantioselectivity was found to be moderate (Table 1, Scheme 1. Aminoxylation of aldehydes via enamine intermediates. a) Previous work by Sibi and Hasegawa, [5] and b) this work. SET = single electron transfer. ee [%][c]

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