Base cleavage of the benzyl−silicon bond in PhCH2SiMe2(CH2)nOH (n = 2 or 3) compounds

Eaborn, Colin; Mahmoud, Foad M.S.

doi:10.1016/s0022-328x(00)88969-x

Cited by 10 publications

(3 citation statements)

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“…t, J = 5.0 Hz), 1.43 (1H, t, J = 6.0 Hz); 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) δ 144.6, 133.2, 130.7, 79.6, 62.9. Spectroscopic data are in agreement with the literature . To a solution of (2 E ,4 E )-5-iodopenta-2,4-dien-1-ol (370 mg, 1.76 mmol, 1.0 equiv) and scandium(III) triflate (130 mg, 264 μmol, 0.15 equiv) in toluene (11 mL) was added 4-methoxybenzyl 2,2,2-trichloroacetimidate (0.55 mL, 2.7 mmol, 1.5 equiv).…”

Section: Experimental Sectionsupporting

confidence: 87%

“…Under methanolysis conditions (Scheme a), attack of methoxide on the acetate leads to a tetrahedral intermediate 21 , the alkoxide derived from which may be ideally placed to engage with the adjacent silicon atom, promoting benzyl cleavage ( 22 ); indeed, the enhanced rate of cleavage of trialkylbenzylsilanes by proximal alcohols had been noted by Eaborn but is rarely exploited . As no debenzylation/cyclization is observed for alcohol 11a under the same conditions, the proximity of the alkoxide (released on ester hydrolysis) to the silicon atom appears to be important. , Upon treatment of 11b with TBAF (Scheme b), the silanol generated by benzyl cleavage ( 23 ) could undergo transesterification with the adjacent acetate, the liberated alkoxide(or alcohol) then cyclizing onto the acetoxysilane. The efficient and rapid cyclization of alcohols 11a / 12a upon treatment with KOTMS (Scheme c), but not of silyl ethers 11c / 12c , implies that a proximal alcohol is beneficial for this unusual debenzylation.…”

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confidence: 99%

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Synthesis of Cyclic Alkenyl Dimethylsiloxanes from Alkynyl Benzyldimethylsilanes and Application in Polyene Synthesis

et al. 2019

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Cyclic dimethylalkenylsiloxanes, useful motifs for (Z)-selective Hiyama cross-coupling, are accessed from alkynyl benzyldimethylsilanes featuring adjacent allylic or homoallylic oxygen substituents by semihydrogenation/ debenzylation/cyclization. While formation of 5-and 6membered rings can be achieved from the free alcohols using fluoride or silanolate, allylic acetate precursors to 5-membered rings display distinct modes of activation. The utility of these compounds is demonstrated through the preparation of a variety of (Z)-alkene-containing polyenes and application to a concise total synthesis of leukotriene B 3 .

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Section: Experimental Sectionsupporting

confidence: 87%

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confidence: 99%

Synthesis of Cyclic Alkenyl Dimethylsiloxanes from Alkynyl Benzyldimethylsilanes and Application in Polyene Synthesis

et al. 2019

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“…8) to make the R group into a carbon nucleophile. 4 We now report a case where the presence of an oxyanion makes a silyl group behave more like a stannyl group, in a reaction with precedent only with a 1,2-Brook rearrangement from an aoxyanion rather than a g-oxyanion. 5 b-Stannyl aldehydes and ketones 6 form cyclopropanols on treatment with Lewis acids (9 ?…”

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confidence: 91%

Unusual cyclopropanol formation from a β-silyl aldehyde

Fleming¹,

Mandal²

1999

Chem. Commun.

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Oligosaccharide Analogues of Polysaccharides. Part 3. A new protecting group for alkynes: Orthogonally protected dialkynes

Cai

Vasella

1995

Helvetica Chimica Acta

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(30. I. 9 5 ) Dialkyncs of the type 3 (Scheme I) are regioselectively deprotected by treating them either with base in a protic solvent (+ 4), or --after exposing the OH group -by catalytic amounts of base in an aprotic solvent (+ 5 and 8).The Me&-protected 12 (Scheme 2) is inert to catalytic BuLi/THF which transformed 11 into 9, while K2C03/ MeOH transformed both 10 into 9, and 12 into 13, evidencing the requirement for a more hindered (hydroxypropy1)silyl substituent. C-Silylation of the carbanions derived from 17-19 (Scheme 3) with 15 led to 20-22, but only 22 was obtained in reasonable yields Main by-product was the dimer 43. On the one hand, K2C0,/MeOH removed the Me& group and transformed 3 9 4 2 into the monoprotected 4447; catalytic BuLi/THF, on the other hand, transformed the alcohols 4851, obtained by hydrolysis of 3942, into the monoprotected dialkynes 52-55, all steps proceeding in high yields. Addition ofthe protected DOPSA groups to the lactones 56 (+ 57-59) and 62 (+ 63) (Schemes 5 and 6 ) gave the corresponding hemiketals. Reductive dehydroxylation of 57 and 58 failed; but similar treatment of 59 yielded the alcohol 61. Similarly, 63 was transformed into 64 which was protected as the tetrahydropyranyl (Thp) ether 65. In an optimized procedure, 62 was treated sequentially with lithiated 31, BuLi, and Me,SiCI (-,66), followed by desilyloxylation to yield 60% of 67, which was protected as the Tbp ether 68. Under basic, protic conditions, 68 yielded the monoprotected bisacetylene 69; under basic, aprotic conditions, 67 led to the monoprotected bisacetylene 70. These procedures are compatible with the butadiynediyl function. The butadiyne 73 was prepared by cross-coupling the alkyne 69 and the iodoalkyne 71 (obtained from 70, together with the triiodide 72) and either transformed to the monosilylated 76 or, via 77, to the rnonosilylated 78. Formation of the homodimers 74 and 75 was grcatly reduced by optimizing the conditions of cross-coupling of alkynes.Introduction. -O m projected synthesis of oligosaccharide analogues of polysaccharides [ 13 requires the regioselective desilylation [2] of protected monosaccharide-or oligosaccharide-derived diacetylenes of the type represented by compounds 1 and 2. We have already described a reagent-controlled, regioselective desilylation of 1, based on the different reactivities of the two Me,SiCrC groups [2]. The Me,SiC=C groups attached at C(6) of 1 and the equivalent moiety in 2 (attached at C(8')) were segioselectively desilylated in 96 and 69% yield, respectively, using the same mild conditions (CN-/ AgNO, [3] [4]). The conditions for the regioselective desilylation of the propargylic ether moiety of 1 (2 equiv. of BuLi/THF; 90%), however, failed with 2 on account of the labile

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Base cleavage of the benzyl−silicon bond in PhCH2SiMe2(CH2)nOH (n = 2 or 3) compounds

Cited by 10 publications

References 4 publications

Synthesis of Cyclic Alkenyl Dimethylsiloxanes from Alkynyl Benzyldimethylsilanes and Application in Polyene Synthesis

Synthesis of Cyclic Alkenyl Dimethylsiloxanes from Alkynyl Benzyldimethylsilanes and Application in Polyene Synthesis

Unusual cyclopropanol formation from a β-silyl aldehyde

Oligosaccharide Analogues of Polysaccharides. Part 3. A new protecting group for alkynes: Orthogonally protected dialkynes

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