Ethyl tritylation

Ertas and Seebach " have studied the synr-anti isomerization of aldol adducts chelated to aluminum for the reaction of ethyl trityl ketone with aldehydes in the presence of trimethylaluminum (Scheme 52). 

Compound 89 was converted into 91 through epimerization at C5 of the ketone 90. The aldehyde 93 reacted with the lithium enolate of ethyl trityl ketone to give the desired aldol 94 as a sole product, which was converted into the (R)-sulfoxide 95 through the epimerization of the (S)-sulfoxide. The lithiated 95 was added to the ketone 91, followed by desulfurization and desilylation, to give the adduct 96. The seco-acid derived from 96 was cyclized by Corey s method followed by deprotection to give (9S)-9-dihydroerythronolide B, which was converted to erythronolide B (55) after 3,5-0-benzylidenation, oxidation and debenzylidenation. 

N,0-Transtritylation. Ethanol allowed to react with N-tritylethanolamine hydrochloride ethyl trityl ether. Y 93%. F. e., also O-transtritylation, s. K. Kor-mendy and M. M. El-Sawy, Acta Chim. Acad. Sci. Hung. 83 (1), 107 (1974) (Eng) C. A. 82, 72497. 

As previously discussed, ethyl chlorocarbonate reacts rapidly and selectively with an equatorial 3-hydroxyl group to give the corresponding cathylate. Trityl ethers, usually employed as a selective protecting group for primary hydroxyls, can be prepared from A -3j3-ols by heating with triphenylmethyl chloride in pyridine, and from 5a-3 -alcohols by more prolonged heat-... 

Attempts to prepare 2-aminoazepinium salts by the action of trityl tetrafluoroborate on azepin-2-amines, e.g. 18, resulted in ring contraction to stable 2-azabicyclo[4.1.0]hepta-2.4-dienium salts, e.g. 3-(pyrrolidin-l-yl)-7-trityl-2-azabicyclo[4.1,0]hcpta-2,4-dicnium tetrafluoroborate (19), the valence isomers of 7-(dialkylamino)-3-trityl-3//-azepinium tetrafluoroborates 64 with Meerwein s reagent the 2-ethyl derivative (77%) is formed. 

The following abbreviations are commonly used for substituent groups in structural formulae Ac (acetyl), Bn or PhCH2 (benzyl), Bz or PhCO (benzoyl), Et (ethyl), Me (methyl), Me3Si (not TMS) (trimethylsilyl), Bu Me2Si (not TBDMS) (rerf-butyldimethylsilyl), Ph (phenyl), Tf (triflyl = trifluoromethanesulfonyl), Ts (tosyl = toluene-p-sulfonyl), Tr (trityl). 

In the second procedure13 (see Scheme 3), D-glucitol (10) was converted into 5-O-benzoyl-1,3 2,4-di-O-ethyl idene-6-O-trityl-D-glucitol (17) by successive treatment with acetaldehyde to produce 15, with chlorotriphenylmethane to provide 16, and with benzoyl chloride to afford 17. Selective removal of the trityl protecting group from 17, to give 18, followed by oxidation of 18, provided 19 which, on hydrolysis, afforded L-gulose (9). 

The earlier paper (Subira et al., 1976) contains results on isobutyl vinyl ether (IBVE) which are republished together with new measurements on methyl (MVE)-, ethyl (EVE)-, and isopropyl (IPVE)-vinyl ethers in CH2C12 over the temperature range 0 °C to -40 °C with m = (2-15) x 10"2, [Ph3CSbCl6] = (5.5-8) x 10"5 mold 1 (Subira et al., 1988). The rate of disappearance of the Ph3C+ ion in the presence of the monomer is considerably smaller than the rate of consumption of the monomer under all conditions, and as mentioned above, the authors identify the rate of disappearance of the trityl cation with the rate of initiation, in our notation... 

To verify such a steric effect a quantitative structure-property relationship study (QSPR) on a series of distinct solute-selector pairs, namely various DNB-amino acid/quinine carbamate CSPpairs with different carbamate residues (Rso) and distinct amino acid residues (Rsa), has been set up [59], To provide a quantitative measure of the effect of the steric bulkiness on the separation factors within this solute-selector series, a-values were correlated by multiple linear and nonlinear regression analysis with the Taft s steric parameter Es that represents a quantitative estimation of the steric bulkiness of a substituent (Note s,sa indicates the independent variable describing the bulkiness of the amino acid residue and i s.so that of the carbamate residue). For example, the steric bulkiness increases in the order methyl < ethyl < n-propyl < n-butyl < i-propyl < cyclohexyl < -butyl < iec.-butyl < t-butyl < 1-adamantyl < phenyl < trityl and simultaneously, the s drops from -1.24 to -6.03. In other words, the smaller the Es, the more bulky is the substituent. The obtained QSPR equation reads as follows ... 

The following abbreviations are used in this and the subsequent tables Ac for acetyl, Pr for propionyl, Bu for butyryl, Bz for benzoyl, Ts for tosyl, My for methylene, Ed for ethylidene, Bd for benzylidene, Fd for furfurylidene. Id for isopropylidene, Me for methyl, Et for ethyl, Be for benzyl, Tr for trityl and Az for azoyl. Where the linkages of acetals and ketals are known, they are shown by different type fonts.)... 

A concise synthesis of tetra-O-ethyl aldonolactam 83 starting from 1 has been reported [102]. After protection of its primary alcoholic moiety as a trityl ether, saponification and treatment with EtBr generated 80. Acidic hydrolysis liberated 81 that was esterified (tosylate). The latter was displaced with NaNs to give azide 82. Reduction of 82 resulted in lactam 83 (Scheme 24). 

Ethyl 1-thio /J-maltoside 6 -0-trityl-hexa-O-acetyl- 101-103 + 71 C 44... 

Norephedrine, 200 Organoaluminum reagents, 202 Organotitanium reagents, 213 9-(Phenylseleno)-9-borabicyclo-[3.3.1]nonane, 245 Tin(II) chloride, 298 Titanium(IV) chloride, 304 Trityllithium, 338 Trityl perchlorate, 339 Zinc chloride, 349 By other reactions Chloromethyl ethyl ether, 75 Dibutyltin oxide, 95 Samarium(II) iodide, 270 Tributyltin hydride, 316 Hydroxy amides a-Hydroxy amides... 

Abbreviations AllocOSu, allyloxycarbonyl-A-hydroxysuccinimide BCIP, 5-bromoA-chloro-3-indolyl Boc, tert-butyloxycarbonyl tBu, tert-butyl DCM, dichloromethane Dde, l-(4,4-dimethyl-2,6-dioxocyclohex-l-ylidene)ethyl Ddz, a, a-dimethyl-3,5-dimethoxyben-zyloxycarbonyl DIC, A,A -diisopropylcarbodiimide DIEA, A,fV-diisopropylethylamine DMF, iV,./V-dimethylformamide FmocOSu, 9-fluorenylmethyloxycarbonyl-AMiydroxysucci-nimide OBOC, one-bead one-compound PBS, phosphate-buffered saline Pmc, 2,2,5,7,8-pentamethylchroman-6-sulfonyl PTH, phenylthiohydantoin RR, relative reactivities Teoc, 2-(trimethylsilyl)ethoxycarbonyl TFA, trifluoroacetic acid Trt, trityl. 

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