Thiols were effectively oxidized into disulfides by reacting with hydrogen peroxide in the presence of a catalytic amount of iodide ion or iodine.The controlled oxidative coupling of thiols to disulfides is important in organic synthesis, and a wide range of methods have been developed for this transformation. 1 Thiols are among the functional groups which can be easily over oxidized, therefore, extensive studies have been carried out for their controlled oxidation with molecular oxygen, 2 peroxide, 3 metal oxidants, 4 halogens and derivatives, 5 sulfoxide, 6 and N-oxide. 7 In particular, the methods of oxidative coupling of disulfides with halogens such as I 2 , 5a I 2 /HI, 5b and Br 2 /KHCO 3 5c were carried out under mild reaction conditions, and gave the disulfides in good yields. However, these reactions require a stoichiometric amount of oxidants and long reaction times. Oae and co-workers developed the oxidative coupling of thiols to disulfides by dimethyl sulfoxide in the presence of a catalytic amount of molecular iodine. 5b Although this reaction affords the products in high yield under very mild reaction conditions, there are still some problems such as the requirement of a long reaction time and the production of foulsmelling dimethyl sulfide as a waste product.To develop an environmentally benign oxidative coupling of thiols, we planned to use hydrogen peroxide as a cooxidant for the oxidation of thiols with molecular iodine, because the iodide ion (iodoanion) is easily oxidized to molecular iodine by hydrogen peroxide.Hydrogen peroxide itself can oxidize thiols to the corresponding disulfides; however, alkaline conditions were required. 3a Recently, Bégué et al. reported that disulfides can be efficiently prepared from thiols using 30% hydrogen peroxide in fluoroalcohols at ambient temperature under neutral conditions. 3b Although this method provides the desired compounds in high yields in most cases, fluoroalcohols are expensive for industrial use. Furthermore, the thiols, which are less soluble in the fluoroalcohols, produced the desired disulfides in poor yields. In this paper, we describe a method for the oxidation of thiols 1 to disulfides 2 using 30% hydrogen peroxide catalyzed by iodide ion (Scheme 1). Scheme 1
Mating behavior of the scarab beetle Dasylepida ishigakiensis was observed in a sugar cane field in Miyako Is., Okinawa, Japan. In field observations of tethered females on 6 February 2002, calling behaviors were observed only within 30 min of sunset time (18:25-18:55, JST), when light intensity decreased from ca. 500 lx to 1 lx. Mating was strongly affected by temperature: adults appeared and subsequent mating occurred when the temperature at 18:00 was higher than 18°C. Females appeared from the soil, flew to settle on sugar cane leaves and commenced rhythmical abdominal expansion and contraction. Males were attracted to the calling females from leeward, landed on or near the calling female, and immediately mounted. After genital connection, the male raised his legs and suspended himself with his genitalia. Mating lasted for ca 2 h. Most mated D. ishigakiensis females neither appeared from the soil nor attracted males until the end of March, so are considered monogamous. In contrast, males appeared from the soil after mating on evenings warmer than 18°C and probably repeat mating if females are available.
The life history of the white grub Dasylepida sp. was surveyed in a sugarcane field in Miyako Is., Okinawa, Japan. Adult flights were observed from early February to mid-March in 2001. Adults commenced flight just after sunset (at around 18:30) and mated. Sampling from the pots placed in the field on 19 April yielded 41.8% eggs and 58.2% first stadium larvae. Larvae sampled on 20 June, 2000 were found to consist of 33.3% and 66.7% of the first and second stadium larvae, respectively. On 22 August, 87.5% of larvae were second stadium and the remainder (12.5%) were third stadium larvae. The proportion of third stadium larvae increased and attained 100% by 30 November. In an excavation survey on 26 November, 2001, 11 adults (three females and eight males) and five pupae were found in the soil at a depth of around 45 cm. Pupae were found in the tunnel cavities. We believe that adults remain in the tunnels until the next February. In the rearing experiments at 25°C in the laboratory, the egg period was 23.6 d and the larval periods of the first, second and third stadia were 80.9, 91.8 and 335.8 d, respectively. These facts indicated that Dasylepida sp. has a two-year life cycle.
The brown planthoppers (BPH) Nilaparvata lugens (Stål) and the white-backed planthoppers (WBPH) Sogatella furcifera (Horváth) annually migrate from tropical and subtropical regions to temperate regions in Asia, including Japan, Korea and northern China. To elucidate the genetic divergence based on geography of planthoppers and to estimate their migration route on the basis of molecular data, we analysed a part of their mitochondrial genome sequences. Sequences of cytochrome oxidase subunit I (cox1) - transfer RNA for Leu (trnL2) - cox2 were determined for 579 BPH (1,928 bp) and 464 WBPH (1,927 bp) individuals collected from 31 and 25 locations, respectively, in East and Southeast Asia. Thirty and 20 mitochondrial haplotypes were detected for BPH and WBPH, respectively. Single populations of both planthoppers included multiple haplotypes, and many haplotypes were shared in some populations and areas. The most frequently detected haplotypes accounted for approximately 50% of all BPH and WBPH individuals. To evaluate gene flow among planthoppers in different regions in Asia, pairwise fixation index (Fst) values were calculated. For BPH, high Fst values (0.580-0.926) were shown between planthoppers in Papua New Guinea (PNG) and the other areas and moderate Fst values (0.176-0.362) were observed between those in southern Philippines and other areas. For WBPH, the Fst value was the highest between Taiwan and southern Vietnam (0.236), and low among the other areas. AMOVA indicated no genetic structure among eight areas, excluding southern Philippines and PNG, for BPH, and among ten areas for WBPH. These data indicate that both planthoppers do not show much differentiation of local populations and/or have genetically intermixed Asian populations. These data also indicate that it may be difficult to distinguish regional planthopper populations on the basis of differences in mitochondrial sequences.
Chemical components that attract males in the laboratory were extracted from the female elytra of the white-spotted longicorn beetle, Anoplophora malasiaca (Thomson) (Coleoptera: Cerambycidae), and found to be comprised of several sesquiterpene hydrocarbons. Males located females that had fed on the bark of the host plant Citrus unshiu more frequently than those fed on an artificial diet in the laboratory. Male attraction was also confirmed in the corresponding sesquiterpene fractions of the host plant. The sesquiterpene fractions of female elytra and C. unshiu leaves showed quite similar GC profiles. In the field, the beetles were found on C. unshiu trees baited with intact females or males as frequently as those baited with the leaf extracts containing the sesquiterpenes at different purification levels. The beetles were found on those baited trees significantly more frequently than on unbaited control trees. Males, as well as females attracted both sexes, and the male elytra also contained the sesquiterpenes that were identical with those in female and C. unshiu. This indicated that active components in the elytra are acquired from C. unshiu by feeding, contact and/or adsorption. These sesquiterpenes may serve for intraspecific communication in A. malasiaca. The major sesquiterpenes from the C. unshiu leaves were isolated and elucidated by NMR analyses of four sesquiterpene hydrocarbons, b-elemene, b-caryophyllene, a-humulene, and a-farnesene.
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