Selenides, trimethylsilyl

Free intermediate thioaldehydes 598 or 602 and the selenoaldehydes 605 and HMDSO 7 are obtained in THF at 0°C on treatment of aliphatic and aromatic aldehydes with bis(trimethylsilyl)thiane 601 or bis(trimethylsilyl)selenide 604 in the presence of traces of butyllithium, while trapping the sensitive intermediate thio- or selenoaldehydes 602 and 605 with cyclopentadiene or cyclohexadiene to furnish mixtures of endo and exo Diels-Alder adducts such as 603 a and 606 a and 603 b and 603 b [148-150], the exo/endo ratio of which can be controlled [150] (Scheme 5.48). Analogous reaction of ketones such as 2-adamantanone or acetylene ketones with MesSiXSiMes 608 (a. X=S (601) b. X=Se (604)) in the presence of... 

CoCl2 6H20 [149] or TMSOTf 20 [150-152] in acetonitrile afford Diels-Alder adducts in yields of up to 85%. The dienals 607 are converted by bis(trimethyl-silyl)thiane 601 or bis(trimethylsilyl)selenide 604 and catalytic amounts of BuLi, via 609, to the intramolecular Diels-Alder products 610 in up to 70% yield [153, 154]. 

In the presence of catalytic amounts of Bp3.0Et2 aromatic aldehydes such as benzaldehyde are converted by bis(trimethylsilyl)selenide 604 into hexamethyldi-siloxane 7 and the corresponding trimers, for example 611 in up to 90% yield. On heating with 1,3-dienes such as 2,3-dimethylbutadiene trimers such as 611 react to give the Diels-Alder product 612 [155] (Scheme 5.49). 

Amides such as DMF or ureas such as N,N-tetramethylurea react with bis(trimethylsilyl)selenide 604 in the presence of BF3-OEt2 to give selenoamides, for example 617, or selenoureas whereas esters such as n-butyl benzoate react with 604 in the presence of Bp3-Et20 and 2,3-dimethylbutadiene to give 619 via 618 [157]. On heating with P4Sio/sulfur and hexamethyldisiloxane 7 y9-ketoesters such as ethyl acetoacetate are converted to 3H-l,2-dithiole-3-thiones such as 620 in high yields [158] (Scheme 5.51 cf. also Section 8.6). 

Entry 5 is an example of the use of fra-(trimethylsilyl)silane as the chain carrier. Entries 6 to 11 show additions of radicals from organomercury reagents to substituted alkenes. In general, the stereochemistry of these reactions is determined by reactant conformation and steric approach control. In Entry 9, for example, addition is from the exo face of the norbornyl ring. Entry 12 is an example of addition of an acyl radical from a selenide. These reactions are subject to competition from decarbonylation, but the relatively slow decarbonylation of aroyl radicals (see Part A, Table 11.3) favors addition in this case. 

Synthesis of 31 by Method I (107,108) and its conversion to the related anti and syn diol epoxide derivatives (32,33) has been reported (108). The isomeric trans-1,lOb-dihydrodiot 37) and the corresponding anti and syn diol epoxide isomers (38,39) have also been prepared (108) (Figure 19). Synthesis of 37 from 2,3-dihydro-fluoranthene (109) could not be accomplished by Prevost oxidation. An alternative route involving conversion of 2,3-dihydrofluoranthene to the i8-tetrahydrodiol (3-J) with OsO followed by dehydration, silylation, and oxidation with peracid gave the Ot-hydroxyketone 35. The trimethylsilyl ether derivative of the latter underwent stereoselective phenylselenylation to yield 36. Reduction of 3 with LiAlH, followed by oxidative elimination of the selenide function afforded 3J. Epoxidation of 37 with t-BuOOH/VO(acac) and de-silylation gave 38, while epoxidation of the acetate of JJ and deacetylation furnished 39. 

Primary selenoamides are prepared by reaction of nitriles with appropriate selenating reagent, such as phosphorus (V) selenide (P2Se5), hydrogen selenide (H2Se), Al2Se3, NaSeH, trw(trimethylsilyl)monoselenophosphate or potassium selenobenzoate (Scheme 81).248 252... 

Selenoaldehydes,2 In the presence of 5-10 mole% of butyllithium, this disilyl selenide converts aldehydes into selenoaldehydes with formation of the disiloxane [(CH,)3SiOSi(CH3),]. The active reagent is presumed to be lithium trimethylsilyl-selenide, (CH3)3SiSeLi, which can be regenerated by a Peterson-type elimination (equation I). 

The radical source must have some functional group X that can be abstracted by trialkylstannyl radicals. In addition to halides, both thiono esters and selenides are reactive. Allyl tris(trimethylsilyl)silane can also react similarly.232 Scheme 10.11 illustrates allylation by reaction of radical intermediates with allylstannanes. 

A higher level of size and morphology control in the incipient semiconductors has been accomplished in reversed micelles prepared from cadmium AOT [614] and from mixtures of cadmium AOT and sodium AOT [615] or, alternatively, by arresting particle growth by surface derivatization [592, 621, 622]. Indeed, surface derivatization of semiconductor clusters was first reported for particles in reversed micelles [621] the reversed micelles act to confine precursor ions and to control the growth of the semiconductor particles. Conditions are typically arranged so that, initially, there is no more than one metal ion (say Cd2+) per water pool. Addition of a heptane solution of bis(trimethylsilyl) selenium resulted in the formation of size-quantized metal selenide particles (say CdSe) in the reversed micelles. This solution could be evaporated to dryness and the resultant particles could be reconstituted in a hydrocarbon solvent Alternatively, addition of metal (say Cd2+) ions to the reversed-micelle-entrapped metal selenide particles, followed by the addition of alkyl(trimethylsilyl)selenium, RMSiMe3, led to the formation of alkyl-capped... 

Reaction of (trimethylsilyl)vinyl selenide 122 with methyl vinyl ketone catalyzed by SnCLt gives the [2 + 2] adduct 123 in 66% yield (equation 51)176. Replacement of the MegSi group with a hydrogen atom or a methyl group produces a complex mixture. Thus, the MesSi group can suppress side reactions by its steric effect. 

Pentacarbonyl(trimethylsilyl)manganese. VINYL FLUORIDES Pyridinium poly(hydrogen fluorideV-N-Bromosuccinimide. VINYLPHOSPHINES 2,4,6-Trii sopropy I benzenesulfonylhy drazine. VINYL SELENIDES Benzeneselenenyl halide-Silver nitrite. Diphosphorus tetraiodide. 

Terminal alkynes reacted in a different way with DIB and diphenyl diselenide, yielding phenyl alkynyl selenides in varying yield, from 81%, for phenylselenyl phenylacetylene, to 15% for trimethylsilyl phenylselenyl acetylene. It is noteworthy... 

Also widely employed are organoselenium compounds containing group 14 elements. Phenyl trimethylsilyl selenide 102 can be easily prepared from diphenyl diselenide 8 and is a good source for selenium nucleophiles (Scheme 24). In the presence of methanol selenols are generated for use in Michael reactions or in ring-... 

A. HEXAMETHYLD1SILASELENANE AND HEXAMETHYLDISILATEL-LURANE, [ BIS (TRIMETHYLSILYL) SELENIDE AND BIS (TRIMETHYLSILYL) TELLURIDE]... 

---