Alternate synthesis using trimethyl

Alternative Routes to Substituted (2-Phenylsulfonylethyl)-trimethylsilanes. Although the fluoride-induced elimination is a reliable and efficient method for synthesizing alkenes, the requisite silyl sulfone precursors are often better prepared by methods which avoid the use of (2). For example, eq 3 illustrates an alternative synthesis of 2,2-dialkyl-2-(phenylsulfonylethyl)trimethyl-silanes involving alkylation of a lithio sulfone with (iodomethyl)-trimethylsilane. ... 

In an alternate synthesis, trimethyl orthoformate (TMOF) is used as the methoxy source, as shown in equation 7 below ... 

The />-nitrobenzylmethoxy group and the l-[(trimethylsilyl)ethoxy]ethyl group have been introduced for hydroxyl protection, especially 2 -OH in solid-phase oligoribonucleoside synthesis. The low yields achieved in the preparation of the diastereomeric pyruvic acid acetals 14 from the corresponding 3,4-di-O-trimethyl-silyl ether 12 by use of the established procedure prompted the authors to devise an alternative route to 14 via the acetoxyacetonide 13, as shown in Scheme 1. The pyruvic acid acetal imidate 15 was obtained in 4 steps from 5-phenyl 4 ,6 -0-benzylidene-l-thiolactoside for use in the synthesis of pyruvated trisaccharides. New examples of the concomitant acetal formation and introduction of a carbamoyl function on treatment of cw-/ranj-configured 1,2,3-triols with chloral/ DCC (e.g., 16 17, see Vol. 28, p. 97, Refs. 16-18) have been reported. 

Monohydrolysis of trimethyl esters is the key to two alternative deterministic approaches as described in Reaction Scheme 6.3 [35]. About 50 % overall yield of cholesteric GLCs, (23) and (24), using pig liver enzyme as the first step in Approach (a), and a 23 % overall yield of (25) involved base catalysis in Approach (b), the former being superior to statistical synthesis with much less laborious work-up procedures. 

The chemical operations described in the literature to introduce or into citric acid molecule are based essentially on the Grimaux and Adam synthesis. Labeled citric acid was prepared by Wilcox et al. [35] in the reaction of Na CN with 3-chloro-2-carboxy-2-hydroxybutyric acid and the formed nitrile was hydrolyzed directly with hydrochloric acid. From this solution, citric acid was isolated in the form of calcium citrate and finally converted to the acid. An alternative procedme was proposed by Rothchild and Fields [36] to obtain trimethyl citrate from labeled sodium cyanide and di-chloromethyl glycolate. A more complex synthesis of C labeled citric acid is described by Winkel et al. [39]. They used labeled methyl acetate and acetyl chloride (in the presence of hthium 1,1,1,3,3,3,-hexamethyldisilazide, [(CH3)2Si]2NLi which was dissolved in tetrahydiofuran) to obtain methyl acetoac-etate. It reacts in the presence of lithium diisopropylamide, [(CH3)2CH]2NLi, also dissolved in tetrahydrofuran, with dimethyl carbonate to give dimethyl 1,3-ace-tonedicaiboxylate. It is dicarboxylated by the action of bisulfite and potassium cyanide is converted to 3-cyano-3-hydroxy-l,5 pentanedioate and finally hydrolyzed by hydrochloric acid to citric acid. 

Sakakura et al. (150) have investigated the use of SCCO2 for the selective synthesis of dimethyl carbonate (DMC) by reaction of CO2 with trimethyl orthoacetate, which also produces methyl acetate (AcOMe) as a byproduct and dimethyl ether as a side product (Scheme 5). A primary incentive of this study was to evaluate the use of SCCO2 as an alternative to phosgene for this reaction. Various metal alkoxides with and without promoters were evaluated as catalytic systems, and the reaction was found to be strongly dependent on the alkox-... 

---