Treatment of Gems

Aquamarine turned from green to blue by heat Yes No No 

Zircon heated to turn colorless or blue Almost all No, but these colors are No 

Sapphire or ruby heated to remove silk Yes Usually Yes 

Sapphire heated to modify or develop a blue color Yes Usually Yes 

Topaz or sapphire irradiated to a yellow or brown color No No, only fact of fading Explained 

---

Finally, Tanabe and coworkers reported that treatment of gem-dichlorocyclopropanes with methylmagnesium bromide in the presence of 5% Fe(dbm)3 and 4-methoxytolnene (1 equiv.) affords the dimethylated product (Scheme 52). 

Treatment of gem-dibromocyclopropane 34 with Bu3ZnLi from —85 to 0°C generates 1-butylcyclopropylzinc 36 via the 1,2-migration of the zincate carbenoid 35 (equation 27)24. Subsequent Pd°-catalyzed cross-coupling reactions afford cyclopropane... 

Japanese chemists have now reported the alkylation of 1-lithiocyclopropyl bromides, prepared by treatment of gem-dibromocyclopropanes with n-butyl-IIIIlium, by reaction with an alkyl halide. They were able to prepare syn-1-niolhyl- nrt-7-bromonorcarane (3) as the exclusive product by addition of methyl Iodide to (2), prepared essentially by Seyferth s procedure. As applied to Ollier gem-dibromocyclopropanes, the reaction is usually stereoselective rather... 

Substitution reactions of simple sulphenyl chlorides with features of additional interest include 1,3-dithiolan formation by reaction of 1,2-disulphenyl chlorides at a methylene group o to —CHO formation of cK-chloro- -keto-sulphides from sulphenyl chlorides and adducts of phosphines with 1,2-dicarbonyl compounds free-radical substitution of saturated alkanes by C6CI5SCI and synthesis of aa-dinitroalkyl sulphides by treatment of gem-dinitroalkanes with sulphenyl chlorides in the presence of base. ... 

A different strategy towards <5-functionalized alkynyllithium compounds consists in the treatment of gem-dibromoaDcenes (accessible from the corresponding aldehydes) with an excess of -BuLi. Following this methodology, intermediate 219 was prepared from the dithiane derivative 218 and alkylated with methyl iodide to give the corresponding alkyne 220 (Scheme 2.29) [181]. 

The preparation of these [4-hydroxy-THISs, (1), X = O] by cydization of a-carboxy-N-arylthiobenzimides (5) by treatment with acetic anhydride and triethylamine has been investigated in detail, and the structure has been revised for the compound previously described as 2.3-diphenyl-4-hydroxythiazolium hydroxide inner salt (1, X = 0, R = R = Ph, R = H) (Scheme 5) (3, 10). 4-Hydroxy-THlSs also arise by condensation of gem-dicyanoepoxides with thioamides (Scheme 6) (8). 

The preparation of e/n-difluoro compounds by the oxidative fluorodesul-furization ot 1,3-dithiolanes readily proceeds by treatment with a pyridinium polyhydrogen fluoride-Af-halo compound reagent the latter serves as a bromonium ion source [2], l,3-Dibromo-5,5-dimethylhydantoin is the most effective of several At-halo oxidants. It is believed that /V-halo compounds combine with hydrogen fluoride to generate in situ halogen fluorides, the oxidants. Formation of gem-difluorides from dithiolanes derived from ketones is efficient and rapid, even at -78 °C, whereas the reaction of dithiolanes derived from aldehydes requires higher temperature (0 °C) (equation 4). 

The synthesis of vinylaziridines through reactions between allylic carbenoid reagents and imines (i.e., Darzen-type reactions) was first reported by Mauze in 1980 [13]. Treatment of aldimines or ketimines 16 with gem-chloro(methyl)allyllithium (17) afforded N-substituted vinylaziridines 18 (Scheme 2.6). Similarly, 2,3-trans-N-diphenylphosphinyl-2-vinylaziridines 21 were prepared with good stereoselectivities (trans cis= 10 1 Scheme 2.7) by treatment of a-bromoallyllithium (20) with N-diphenylphosphinyl aldimines 19 in the presence of zinc chloride [14]. 

The antisense oligonucleotide LErafAON against the serine/threonine kinase c-Raf has been tested in phase I clinical trials. The antisense oligonucleotides ISIS-5132, which also inhibits c-Raf, and ISIS-3521, which inhibits PKC, went through different phase clinical trials with solid tumour patients. Unfortunately, no objective responses occurred with these PKI. GEM-231, an oligonucleotide targeting the RIa subunit of protein kinase A is currently undergoing phase I/II clinical trials alone or in combination with traditional therapy for the treatment of solid cancers [3]. 

Analysis of gem treatments comparison of nano-second and pico-second laser-induced breakdown spectroscopy... 

LIBS analysis of gem treatments has several advantages over traditional techniques, including ... 

If appropriate analytical protocols are developed, LIBS will have a place in the field of gem analysis to detect and monitor chemical treatments in the gem trade industry. 

Treatment of the optically active gem-borazirconocene alkanes with deuterium oxide followed by alkaline oxidation affords the corresponding optically active 1-deuterio primary alcohols. The enantiomeric excess of the resulting primary alcohols represents the diaster-eoselectivity of the asymmetric hydrozirconation (Scheme 7.13). Based on the cost and availability of optically active ligands, three types were explored monoterpenes, 1,2-diols, and 1,2-amino alcohols. Hydrozirconation of optically pure 1-alkenyl boranes 39 provided optically active 1,1-bimetallics 40. 

Hydrozirconation of 1-alkynyl pinacolboronates with Cp2Zr(H)Cl provides gem-boriozirco-nocenes 45. Treatment of 45 with CuBr gives the homocoupled (1 fc, 3fc)-2,3-dibora-l,3-dienes 46 in good yield (Scheme 7.15) [92]. The zirconocene-induced coupling was studied using a series of 1-alkynyl pinacolboronates 47. In this case, two regioisomers 48 and 49 were detected (Scheme 7.15). 

From a mechanistic point of view, the titanocene(II)-promoted intramolecular cyclopro-panation of gem-dihalides possessing a terminal double bond is interesting. Although the products of ring-closing metathesis, i. e. cycloalkenes, are produced in certain cases, the treatment of 6,6- and 7,7-dihalo-l-alkenes (e. g. 39 and 40) with titanocene(II) species affords bicyclo[3.1. OJhexane and bicyclo[4.1.0]heptane derivatives 41 and 42, respectively (Scheme 14.19) [34],... 

The treatment of the bromoacetal (255) with catalytic amounts ( 10%) of a Co(I) species, generated by the electroreduction of cobaloxime (232) in an Me0H-LiCl04 system at —1.8 V, produces the cis-fused adduct (256) in 60 70% yield (Scheme 96) [392]. Cathodic reduction is used for the synthesis of a [Co(CO)3PBu3] complex in a methanol-methyl formate medium, which catalyzes the alkoxycarbonylation of dichloromethane to dimethyl mal-onate in up to 75% yield [393]. The Co(II) complexes are found to be effective for the homogeneous reduction of gem-dichlorocyclopropanes in the presence of anthracene [394]. The formation of the C—C double bond of (258) may be ascribed to the a-elimination of the Co-H species. Thus, benzalchloride (257) can be converted to a mixture consisting primarily of ds- and trans-stilbenes (258) by the action of electrogenerated Co(I)(salen) (Scheme 97) [395-398]. 

Many of the nitronate salts of polynitroaliphatic compounds, particularly salts of gem-nitronitronates, exhibit properties similar to known primary explosives. Consequently, the storage of such salts is highly dangerous. Treatment of these nitronate salts with formaldehyde yields the corresponding methylol derivative via the Henry condensation. These methylol... 

Formation of compounds like 115 seems to have occurred in the similar way as it was established for anilines and other primary amines [167]. The initial step of this reaction is treatment of aldehyde with aminozole giving Schiff base 116. Further, nucleophilic attack of imine carbon by mercapto moiety of the acid leads to the intermediate 117 and its subsequent cyclization via gem-diol 118 yields target heterocycles 115 (Scheme 55). 

The first manufacturing route of the GEM side-chain relied on a-cyanoketone 125 however, the number of chemical steps from 125 to the final side-chain was reduced by one step (Noh et ah, 2004a). The sequence began with a selective hydrogenation with Raney nickel followed by double bond migration to enamine 131 (Scheme 4.25). The amino functionality of 131 was then monoprotected, and the double bond was reduced under hydrogenation conditions to afford pyrrolidine-3-one 133. Treatment of 133 with methoxylamine yielded methoxyoxime 129. Deprotection of the carbamate functionality was achieved with methanesulfonic acid to afford the C7-side-chain as the bis-methansulfonate salt. 

According to the vendor, the cost of using GEM-1000 ranges from 30 to 150 (1995 dollars) per ton of media treated. This estimate may not include all indirect costs associated with treatment, such as excavation, permits, and treatment of residuals (D102761). A GEM-1000 unit costs approximately 750,000. In 2001, a second-hand GEM-1000 unit built in 1990 listed for 190,000 (D22267D, p. 1 D22268E, p. 1). 

Finally, gem-difluoromethylene analogs, e.g., 315 and 316, designed to mimic artemisinin, have been prepared by the treatment of the trifluoromethyl derivatives 169 and 173 with 2 equiv of MeLi in THF at —78 °C, and their anti-malarial activity investigated (Scheme 53) <2006JFC637>. 

---