Allyl alcohols trimethylsilyl substituted

The diacetal 629, prepared from the carbonyl compound and O-silylated allylic alcohols in the presence of TMSOTf 20, reacts with ( )-l-trimethylsilyl-2,4-penta-diene 630, in the presence of TMSOTf 20 in CH2CI2 at -78°C, to afford 60% 631 this undergoes Diels-Alder-cyclization at 170 °C in toluene to give a substituted... 

Somei adapted this chemistry to syntheses of (+)-norchanoclavine-I, ( )-chanoclavine-I, ( )-isochanoclavine-I, ( )-agroclavine, and related indoles [243-245, 248]. Extension of this Heck reaction to 7-iodoindoline and 2-methyl-3-buten-2-ol led to a synthesis of the alkaloid annonidine A [247]. In contrast to the uneventful Heck chemistry of allylic alcohols with 4-haloindoles, reaction of thallated indole 186 with 2-methyl-4-trimethylsilyl-3-butyn-2-ol affords an unusual l-oxa-2-sila-3-cyclopentene indole product [249]. Hegedus was also an early pioneer in exploring Heck reactions of haloindoles [250-252], Thus, reaction of 4-bromo-l-(4-toluenesulfonyl)indole (11) under Heck conditions affords 4-substituted indoles 222 [250], Murakami described the same reaction with ethyl acrylate [83], and 2-iodo-5-(and 7-) azaindoles undergo a Heck reaction with methyl acrylate [19]. 

The introduction of the allylic silane moiety required for the intermolec-ular Hosomi-Sakurai reaction is depicted in Scheme 16. Following the formation of the enol triflate 97, a Stille coupling provided excess to the allylic alcohol 98 [51]. The allylic alcohol (98) was endowed with a phosphate leaving group for the subsequent allylic substitution. Utilizing a trimethylsilyl cuprate as nucleophile for the 5 2 reaction, the allylic phosphate was converted into the allylic silane 89. A useful substrate-induced diastereoselectivity in favour of (14i )-89 was encountered at small scale but decreased significantly upon up-scaling. 

Kinetic resolution through Sharpless epoxidation of the trimethylsilyl-substituted allyl alcohol, rac-( )-4-trimethylsilyl-3-buten-2-ol (rac-14), which provides the S-enantiomer [( )-14, see p 476 for chemical correlation]81. 

Allylsilanes. A general synthesis of allylsilanes involves alkylation at the imposition of an allylic alcohol substituted at the 7-position by a trimethylsilyl group or at the a-position by a trimethylsilylmethyl group with an organolithium compound mediated by this phosphonium iodide (l).2... 

Epoxidation of / - or y-trimethylsilyloxy allylic alcohols. The stereoselectivity of cpoxidation of these allylic alcohols (followed by desilylation) can be controlled by substitution with a trimethylsilyl group. A /i-silyl substituted allylic alcohol is converted mainly into an erythro-epoxy alcohol, whereas a y-silyl substituent favors formation of a threo-epoxy alcohol. The stereoselectivity is usually the opposite to that obtained with m-chloroperbenzoic acid.1 Example ... 

Limitations of the reaction due to the substitution pattern of the allylic alcohols were overcome by the use of tetrapropylammonium perruthenate (TRAP) as a catalyst and monosubstituted, disubstituted and trisubstituted allyl alcohols were converted into the corresponding saturated aldehydes and ketones [5]. Intermediacy of the ruthenium alkoxide in this reaction was evidenced from the complete lack of reactivity of the trimethylsilyl ether derived from the allylic alcohol. 

Unfortunately, attempts to perform this substitution reaction on cyclohexenol and geraniol led to the exclusive formation of the corresponding silyl ethers. It thus would seem that one requirement for effective carbon-carbon bond formation is that allylic alcohols be secondary and have possess y,y-disubstitution. Pearson, however, discovered a method with less restriction on the natiue of the substrate he used allylic acetates with y-mono-substitution or primary alcohols [96]. Not only ketene silyl acetals but also a diverse set of nucleophiles including aUyl silane, indoles, MOM vinyl ether, trimethylsilyl azide, trimethylsilyl cyanide, and propargyl silane participate in the substitution of y-aryl allylic alcohol 90 to give allylated 91 (Sch. 45). Further experimental evidence suggests that these reactions proceed via ionization to allylic carboca-tions—alcohols 90 and 92 both afforded the identical product 93. 

Epoxidation of acyclic allyl alcohols with peracid and Mo/TBHP displays an opposite stereospecificity to that for the V/TBHP system. Trimethylsilyl-substituted allylic alcohols give t/zreo-epoxyalcohols with MCPBA and erythro-alcohols with VO(acac)a-TBHP, with high stereoselectivity. In the stereospecific epoxidation of cis- and trans-allyl alcohols, formation of a transition state is assumed with the development of two H bonds between the hydrogen atom of the hydroxy group of the allyl alcohol and the oxygen of the peracid, and between the hydrogen of the peracid OH and the oxygen of the ether 10. An analysis of the diastereometric transition-state interactions for stereoselective epoxidation of acyclic allylic alcohols has been published. A conformational effect may be responsible for the unexpected cis major product in Eq. 2. 

Cathodic coupling reactions of ketones to trimethylsilyl substituted allyl alcohols X... 

Eliminations. When functionalized silanes in which a potential leaving group is attached to a /3-atom or to a vinylogously related atom are treated with TBAF, fragmentation ensues. New uses of this process are preparations of 2,3-dimethylene-2,3-dihydrothiophene," substituted 1,2,3-butatrienes, chiral allylic alcohols, and a-fluoroketones. The precursors for the allylic alcohols are the alkylation products (with aldehydes) of 2-(trimethylsilyl)ethyl sulfoxides, and those for the fluoroketones are 1-silyl-l-hydroxymethyloxiranes. 

The Mitsunobu reaction is one of the staple reactions for clean nucleophilic substitution with inversion of configuration. It came as a surprise, therefore, to find that a Mitsunobu reaction on allylic alcohol 143.1 [Scheme 8.143] using rerr-butyl 2-(trimethylsilyl)ethylsulfonylcarbamate (143.2) as the nucleophile occurred with retention of configuration. o unusual stereochemistry was explained by a double inversion process in which neighbouring group participation first leads to the intermediate 1433. A subsequent second nucleophilic substitution by 1433 then gave the product 143.4 in 86% yield. 

If the oxidation is performed in the presence of an external dienophile, the respective products of [4+2] cycloaddition are formed [351-356]. Typical examples are illustrated by a one-pot synthesis of several silyl bicyclic alkenes 283 by intermolecular Diels-Alder reactions of 4-trimethylsilyl substituted masked o-benzoquinones 282 generated by oxidation of the corresponding 2-methoxyphenols 281 [351] and by the hypervalent iodine-mediated oxidative dearomatization/Diels-Alder cascade reaction of phenols 284 with allyl alcohol affording polycyclic acetals 285 (Scheme 3.118) [352]. This hypervalent iodine-promoted tandem phenolic oxidation/Diels-Alder reaction has been utilized in the stereoselective synthesis of the bacchopetiolone carbocyclic core [353]. 

Ueno has devised a general synthetic method for the preparation of allyltin from allyl sulfones via an Sh2 process [131]. The key steps for these transformations which consist of addition of stannyl radical to appropriate allyl sulfone and the -elimination of sulfonyl radical are depicted in Scheme 17 (see Scheme 11 for detailed propagation steps). Since both steps are reversible, the equilibrium can be driven to the left or right depending on the experimental conditions [132]. However, the extension of this methodology to the synthesis of homoal-lylic alcohols or to 2-substituted-1,3-butadiene have been achieved starting from the appropriate sulfone (Scheme 17) [133]. This approach has also been applied to the preparation of 2-functionalized allyl tris(trimethylsilyl)silanes (cf. equation (38)) [83]. 

A publication surveying uses of trimethylsilyl trifluoromethanesulphonate in synthesis includes the isomerization of epoxides to give allylic alcohols cf. 4, 145) in unsymmetrical cases ring opening occurs at the more substituted epoxide carbon atom (Scheme 14), and the same regiochemistry is observed in... 

Allylic Alcohols. Full details have appeared of the conversion of epoxides into allylic alcohols, mediated by trimethylsilyl trifluoromethanesulphonate (Scheme 4) (see 6,163 4,145), and this sequence is mentioned in a review of trialkylsilyl perfluoroalkanesulphonates as reagents opening of an epoxide ring occurs at the more substituted centre. The use of trimethylsilyl iodide for the epoxide-allyl alcohol transformation (5, 158) is discussed in a review of the preparation and applications of this reagent. ... 

LPDE mediated allylic substitutions have been investigated widely. Substitution reaction of allylic alcohols with silyl ketene acetals, allyl silanes, indoles, methoxymethyl vinyl ether, trimethylsilyl azide, trimethylsilyl cyanide, and propar-gyl silanes proceeds with LPDE (Scheme 3.9) [32, 33]. An experiment with allylic alcohol (5,6) proved that these reaction proceeds via generation of allylic carbocation (Scheme 3.10). Also with a combination of LPDE and AcOH (1 mol%), more efficient allylic substitutions proceed (Scheme 3.11) [34]. 

Several reviews cover hetero-substituted allyllic anion reagents48-56. For the preparation of allylic anions, stabilized by M-substituents, potassium tm-butoxide57 in THF is recommended, since the liberated alcohol does not interfere with many metal exchange reagents. For the preparation of allylic anions from functionalized olefins of medium acidity (pKa 20-35) lithium diisopropylamide, dicyclohexylamide or bis(trimethylsilyl)amide applied in THF or diethyl ether are the standard bases with which to begin. Butyllithium may be applied advantageously after addition of one mole equivalent of TMEDA or 1,2-dimethoxyethane for activation when the functional groups permit it, and when the presence of secondary amines should be avoided. 

Etherification. The reaction of alkyl halides with sugar polyols in the presence of aqueous alkaline reagents generally results in partial etherification. Thus, a tetraallyl ether is formed on reaction of D-mannitol with allyl bromide in the presence of 20% sodium hydroxide at 75°C (124). Treatment of this partial ether with metallic sodium to form an alcoholate, followed by reaction with additional allyl bromide, leads to hexaallyl D-mannitol (125). Complete methylation of D-mannitol occurs, however, by the action of dimethyl sulfate and sodium hydroxide (126). A mixture of tetra- and pentabutyloxymethyl ethers of D-mannitol results from the action of butyl chloromethyl ether (127). Completely substituted trimethylsilyl derivatives of polyols, distillable in vacuo, are prepared by interaction with trimethylchlorosilane in the presence of pyridine (128). Hexavinylmannitol is obtained from D-mannitol and acetylene at 25.31 MPa (250 atm) and 160°C (129). 

A review of intramolecular 4 + 3-cycloadditions of allyl cations has been presented.277 The 4 + 3-cycloaddition reaction of C(2)-substituted furans with 1,3-dimethyloxyallyl cations show high endo diastereoselectivity and a cis dia-stereospecificity.278 The tandem Peterson olefination/[4 + 3]-cycloaddition of tertiary alcohols (149) in the presence of filran and Lewis acids (TiCLt) furnishes cycloheptanes (150) in modest yields (Scheme 57).279 (Trimethylsilyl)methyl allylic sulfones (151) were used to investigate the scope and limitations of intramolecular 4 + 3-cycloadditions of allylic sulfones (Scheme 58).280 Lewis acid-catalysed 4 + 3-... 

A definite improvement in the synthesis of A -methoxy aziridines was achieved by substituting boron trifluoride with trimethylsilyl triflate and diethyl ether with dichloromethane"9. In this way, the A -methoxy aziridines were obtained in good yields from a variety of linear and cyclic alkenes, e.g., 6-8. For comparison, the aziridine 8 was obtained in 50% yield by using boron trifluoride- diethyl ether complex in dichloromethane. Complex product mixtures were obtained with allyl and crotyl alcohols and with cyclohexenone. Further transformation of the A -methoxy aziridines into the N-H aziridines was possible using sodium/ ammonia reduction, e.g., 9. 

Tridentate salen ligands (10) derived from 1 have given excellent results in the enantiocontrol of the hetero Diels-Alder addition reaction of dienes with aldehydes (eq 7) and in the asymmetric additions of TMS-azide to mc5o-epoxide and trimethylsilyl cyanide to benzaldehyde (up to 85% ee). Phosphino-oxazolines derived from 1 have been employed for the asymmetric control of palladium-catalyzed allylic substitution reactions products of 70-90% ee were obtained. Photolysis of crystalline adducts of enantiomerically pure 1 with prochiral alcohols results in asymmetric inductions of up to 79% in a rare example of a solid-state enantioselective reaction. ... 

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