Allylsilanes sulfide

Another interesting example of a photochemi-cally induced domino process is the combination of the photocyclization of aryl vinyl sulfides with an intramolecular addition as described by Dittami et al. [901 as intermediate a thiocarbonyl ylide can be assumed. The domino-Norrish I-Knoevenagel-allyl-silane cyclization developed by us allows the efficient stereoselective formation of 1,2-trans-subsituted five- and six-membered carbocycles.1911 A photochemical cycloaddition of enamino-aldehydes and enamino-ketones with the intermediate formation of an iminium salt followed by addition to allylsilanes gives access to novel bicyclic heterocy-des. New examples of photochemically induced... 

Intramolecular cyclizationlenolate trapping of allylsilanes (cf., 12,496-497).3 The intermediate enolate formed in the TiCl4-catalyzed cyclization of 1 can be trapped by chloromethyl methyl sulfide to give a decalone derivative with a potential methyl group on the angular position. Actually the reaction results in... 

Different nucleophiles such as methanol, allylsilanes, silyl enol ethers, trimethylsilyl-cyanide, and arenes can be used in this process [62]. When the sulfide itself contains an unsaturated or aromatic fragment and the process is carried out in the absence of a nucleophile, an intramolecular anodic sub-stitution/cyclization might occur [61-63]. Methyl esters of 2-benzothiazolyl-2-alkyl or aryl-acetic acid, oxidized in MeOH/Et4 NCIO4 or H2SO4 in the presence of CUCI2, form 2,2-dimethoxy products (Eq. 7) [64]. 

Type I (fast homodimerization) Terminal olefins, allylsilanes" Terminal olefins, allylsilanes," 1° allylic alcohols, ethers, and esters, " allyl boronate esters, allyl halides, alkyl-substituted allenes Terminal olefms, allyl boronate esters, 1° allylic alcohols, ethers, and esters,styrenes (no large ortho substit.), " " allyl allylsilanes, allyl sulfides, allyl phosphonates, " allyl phosphine oxides, protected allylamines ... 

A major advance in this area is represented by the fluoride ion-promoted addition of allylsilanes to thioketones423 (equation 116) giving the compounds arising from a direct thiophilic addition, namely the corresponding allyl sulfides. 

Annelation.1 This reagent is used for conversion of 3-substituted aldehydes (or acetals) into methylenecyclohexanes. The conversion involves addition of the allylsilane group to the aldehyde or acetal to provide an adduct that undergoes radical cyclization via the allylic sulfide group. The phenylthio group is used to enhance 6-endo cyclization over the usual 5-exo cyclization. In addition it allows use of bis(tributyltin) as the initiator (14,173-174). Unfortunately the radical cyclization shows only slight stereoselectivity. 

THF at - 20°. All other anions should be prepared separately, and 2 should be added to 1 at - 20°. By these procedures mono- and disubstituted olefins, vinyl sulfides, vinyl ethers, and allylsilanes are available in 35-80% yield, usually as cis-trans mixtures. Trisubstituted olefins are best prepared by similar routes from a -branched nitrile anions. 

The reaction of 2a with an allylsilane-type sulfide, 3-trimethylsilyl-2-methyl-thio-l-propene (7b), also afforded the cyclobutanes 8b and 9b in 54% (>98% ee) and 17% yields, respectively, without any formation of allylation and ene reaction products. The diastereoselectivity of these two reactions using 2-alkylthio-propene derivatives 7a,b is not high, but the major isomers 8a,b are obtained in nearly enantiomerically pure forms. 

Among nucleophiles used are enols " (including mono- and bis-TMS ethers, which are particularly favorable ) derivatives of P N and S in hydrogen sulfite dithionate and sulfide Si, Ge, Sn and alkyl or aryl in derivatives of Cd, Zn or Li . The Li reagents in particular require special experimental conditions, including dichloro methane as solvent and radical scavengers. Many nucleophiles cause electron addition to the cations, with formation of radicals. Aromatic substitutions displace not only H but SnMej or SiMe3 . Allylsilanes and trialkyl alkynylborates provide synthetically useful products. 

Ailylic oxidation, 64-65 Ailylic sulfides, 176 Allylic thionocarbamates, 201 Allylidenetriphenylphosphorane, 219 a-Allyloxy ketones, 107 ir-Allylpalladium complexes, 385 l-AIlyl-2-phenylcyclopropane, 291 AUylquinone synthetase, 134 Allylsilanes, 509, 510... 

Chiral oxetanes can be synthesized by the BF3-OEt2 catalyzed [2 + 2] cycloaddition reactions of 2,3-O-isopropylidenealdehyde-D-aldose derivatives with allylsilanes, vinyl ethers, or vinyl sulfides. The regiospecificity and stereoselectivity is greater than in the photochemical reaction fra s-2-alkoxy- and trans-2-phenylthiooxetanes are the resulting products. 

Photochemical oxidations of various substrates such as amines [763], alkenes [769,770,772,775,778-780], fiiran [764,765], sulfide [766,773], phytol [767], bi-adamantylidene [768], thiophenolate [771], catechol [774], allylsilane [776], and imines [777], etc., through reactions with singlet oxygen sensitized by porphyrins have been extensively studied. Photochemical atrop isomerization of picket-fence-type porphyrin should be noted here as another interesting type of photoreaction [793]. 

The silyl group and ArS groups are effective for the oxidation of the benzylic position. The anodic oxidation of benzylic sulfides in the presence of allylsilanes takes place smoothly, giving rise to selective C-S bond cleavage and introduction of an allyl group on the benzylic carbon Eq. 11 [15]. 

The anions, generated in situ by desilylation of silylacetylenes, allylsilanes, propargylsilanes, a-silyloxetanones, bis(trimethylsilylmethyl) sulfides, and other silane derivatives,can undergo nucleophilic addition to ketones and aldehydes (eq 11). Al-(C,C-bis(trimethylsilyl)methyl) amido derivatives can add to aldehydes followed by Peterson alkenation to form acyl enamines. Treatment of 2-trimethylsilyl-l,3-dithianes can generate dithianyl anions, which are capable of carbocyclization via direct addition to carbonyl or Michael addition (eq 12). The fluoride-catalyzed Michael additions are more general than Lewis acid-catalyzed reactions and proceed well even for those compounds with enolizable protons and/or severe steric hindrance (eq 13). ... 

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