Methyl methylseleno

Alkylation of disodium selenide telluride with methyl iodide in liquid ammonia produced a mixture of dimethyl diselenium (55%), dimethyl tellurium (10%), and methyl methylseleno tellurium. ... 

The methyl methylseleno tellurium could not be purified by vacuum distillation because the compound decomposed1. 

Selenolo[3,2-h]selenophene (12) and selenolo[2,3-b]selenophene (13) have been synthesized from lithium derivatives of 2-(3-bromo-2-selienienyl) 1,3-dioxane and 2-(3-selenienyl) 1,3-dioxane, respectively, by reaction with selenium and methyl chloroacetate followed by Dieckmann cyclization.46 Even the third classical selenophthene (11) has been synthesized by two different routes, using 2,3-bischloromethyl-5-carbomethoxyselenophene (14) or preferably 4-methylseleno-3-selenophene aldehyde (IS).46 The fourth selenophthene isomer (16), which has a nonclassical structure, has not yet... 

Mercapto-4-methyl- -2-sulfid E2, 710 2-Mercapto- -2-sulfid E2, 710, 767 2-Mercapto-4,4,6-trimcthyl- -2-sulfid XII/2, 687 2-Mcthoxy-4-methyl- E2, 578, 703 2-Methoxy-4-methyl- -2-oxid E2, 578 2-Methoxy-4-methyl-2-phenylimino- E2, 704 2-Methoxy-4-methyl- -2-sulfid E2, 693, 703 aus 2-Methoxy-4-methyl- 1,3,2-dioxaphosphori-nan-2-phenylimid E2, 704 4-Methyl-2-methylseleno- -2-oxid E2, 784 4-Methyl-2-methylthio- -2-sulfid E2, 787 4-Methyl-2-natriumoxy- -2-sulfid E2, 662 4-Methyl-2-(4-nitro-phenoXv)- -2-sulfid E2, 702 2-Methyl- -2-oxid XII/1, 427 2-(4-Methyl-phenyl)- -2-oxid E2, 365 4-Methyl-2-vinylamino- -2-sulfid XII/2, 768 2-Morpholino- -2-oxid El, 514 2-(4-Nitro-phenyl)- -2-oxid E2, 365 2-Phenoxy- -2-oxid XII/2, 346... 

Lithium butyltelluroselenolate is methylated by methyl trifluoromethanesulfonate. The butyl methylseleno tellurium is in equilibrium with dibutyl ditellurium and dimethyl diselenium2. 

Methyl 2-chlorophenyl tellurium was quaternized by excess methyl iodide in refluxing acetone. 1,2-Bis[methyltelluro]benzene formed the ditelluronium compound under these conditions. When the ort/io-substituent in methyl 2-X-phenyl tellurium is a methoxy, methylthio, or methylseleno group that is also capable of quaternization, excess methyl iodide in refluxing acetone quaternizes only the methyltelluro group9. 

The preparation of nine 75Se derivatives of steroids has been described these labelled steroids have proved useful in assaying the comparative binding of proteins.77 Reaction of 75Se02 with dehydroepiandrosterone yields a selenium derivative (183) which upon reduction with dithiothreitol or HSCH2CH2OH and then methylation furnishes the corresponding methylseleno-steroid. 

In this field, Krief and coworkers have also reported that the >-styrenylbenzyllithium derived from l,6-diphenyl-6-(methylseleno)-l-heptene 139 and butyllithiums provides after methanolysis cis- or fraws-2-benzyl-l-methyl-l-phenylcyclopentane 140 with very... 

The reactivity of 8b deserves specific attention. When treated with 2equiv of methyl triflate (in CDCI3), the / -(methylseleno)alkyl phosphonium triflate was obtained as a highly air-sensitive material in 76% yield (Scheme 10) <2002JA9706>. It is reasonable to assume that methyl triflate undergoes an electrophilic attack on the negatively charged selenium center of 8b, and this is followed by dissociation of the polarized Se-P bond (see Section 1.15.3). 

New cyclic methylseleno imino compounds were synthesized from (4/ )-MCTT (I) or D-cysteine methyl ester (154) (Scheme 28) (86JOC4737). 

The presence of a group able to delocalize the charge from the caibanionic center favors the synthesis of the carbanion whatever the method used, whereas substitution of the carbanionic center by alkyl groups disfavors it. Thus, whereas methyl phenyl and dimethyl selenide cannot be metallated wiA LDA at -78 °C or 0 C, phenylseleno and methylseleno acetates and propionates lead, on reaction with the same base at -78 °C, to the corresponding organometallics (Scheme 10). - ... 

The direct selenoacetalization of carbonyl compounds by selenols is by far the shortest and most convenient route to selenoacetals. The reaction is usually carried out at 20 C with zinc chloride (0.5 equiv. versus the carbonyl con x>und) and delivers rapidly (<3 h) and in reasonably good yields methyl and phenyl selenoacetals derived from aliphatic aldehydes and ketones and cyclic ketones (Scheme 69). Selenoacetalization is more difficult to achieve with hindered ketones, such as adamantanone and diisopropyl ketone, and with hindered aromatic carbtmyl compounds. In these cases the reaction is best achieved with titanium tetrachloride instead of zinc chloride and is often limited to the methylseleno derivatives (Scheme 78). Tris(methylseleno)borane offers the advantage of not requiring an acid catalyst and is particularly useful for the selenoacetalization of acid labQe aldehydes such as citronellal (Scheme 70, e). 

Phenylseleno- and methylseleno-alkyllithiums usually exhibit a closely related reactivity towards carbonyl compounds whether the reaction is performed in THF or in ether. As expected, the nudeophilicity of such species often decreases by increasing the substitution around the ct anionic center (6 and 8 Scheme 112), but interestingly they are often far more nucleophilic than the corresponding alkyl-lithiums. However, in some rare cases employing particularly hindered reaction partners there is a significant difference of reactivity between phenyl- and methyl-selenoalkyllithiums when the reactions are performed in THF, since the former reagents are much less nucleophilic than the latter (compare 11 and 12 in Scheme 113 and 17a-17f in Scheme 114). As general trends, a-methylselenoalkyllithiums are more nucleophilic in ether than in THF (compare 15 in Scheme 113.17d and 17e in Scheme 114 and 24 in Scheme 116). 

Methylation of the lithium enolates derived from cyclohexen-2-one and l,l-bis(methylseleno)ethylli-thium t es place regioselectively but requires the use of more than one equivalent of HI A (S equiv., 0 C, 1 h). The product consists quite exclusively of the trans stereoisomer (99%) with a trace (1%) of the cis (Scheme 140, d and e). The latter can be obtained as a single stereoisomer on hydrolysis of the adduct resulting from the reaction of the same organometallics with 2-methylcyclohexen-2-one... 

The reaction between l,l-bis(methylseleno)-l-propyllithium and other methylcyclohexenones has also been investigated (Scheme 131). ° No adduct was obtained ° from 3-methylcyclohexen-2-ones whatever the conditions used (THF-HMPA or DME), whereas 7-keto selenoacetals are produced from 4-, 3-and 6-methyl-2-cyclohexen-2-ones in yields ranging from 38 to 76% when the reactions are carried out in THF-HMPA (Scheme 131). Yields are lowered by 10% when DME is used instead. °... 

The most successful combination involves methylseleno derivatives as starting materials, methyl iodide (neat) as the alkylating agent and 10% aqueous potassium hydroxide solution in ether as the base. In some difficult cases, such as those involving hindered p-hydroxyalkyl selenides, where the... 

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