Methylene blocking group

The formation of a dithioacetal as an intermediate in organic synthesis is not new to most chemists. However, in recent years there has been a continuing improvement in the methods of preparation as well as the subsequent reactions. The early use of the dithioacetal group as a means to reduce carbonyl functions with Raney nickel has been expanded to extensive use as a protecting group, methylene blocking group and as an intermediate in the preparation of complex hydrocarbons, olefins, aldehydes and ketones. 

In the continuing search for the ideal methylene blocking group, considerable effort has been expended in looking at derivatives of hydroxy-methylenes. These are readily prepared from a ketone, ethylformate and sodium methoxide . ... 

Table 2. Alkylation of ketones using thioenol ethers as a methylene blocking group...

A suspension of 0.43 g. 2-amino-2-deoxy-3-0-methyl-L-threitol hydrochloride in methylene chloride treated with BGI3 at —70° for 3 hrs., and allowed to stand overnight at room temp. -> 0.41 g. crude 2-amino-2-deoxy-L-threitol hydrochloride.—0-Methyl blocking groups can be readily removed with BGI3 at low temp. A. B. Foster, Soc. 1960, 2587. 

Properties have been determined for a series of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and poly [3,3-bis(methoxymethyl)oxetane]- (9-tetrahydrofuran. The block copolymers had properties suggestive of a thermoplastic elastomer (308). POX was a good main chain for a weU-developed smectic Hquid crystalline state when cyano- or fluorine-substituted biphenyls were used as mesogenic groups attached through a four-methylene spacer (309,310). Other side-chain Hquid crystalline polyoxetanes were observed with a spacer-separated azo moiety (311) and with laterally attached mesogenic groups (312). 

The standard free energy can be divided up in two ways to explain the mechanism of retention. First, the portions of free energy can be allotted to specific types of molecular interaction that can occur between the solute molecules and the two phases. This approach will be considered later after the subject of molecular interactions has been discussed. The second requires that the molecule is divided into different parts and each part allotted a portion of the standard free energy. With this approach, the contributions made by different parts of the solvent molecule to retention can often be explained. This concept was suggested by Martin [4] many years ago, and can be used to relate molecular structure to solute retention. Initially, it is necessary to choose a molecular group that would be fairly ubiquitous and that could be used as the first building block to develop the correlation. The methylene group (CH2) is the... 

An ATP analog, /3, y-methylene-ATP, in which a —CHg— group replaces the oxygen atom between the /3- and y-phosphorns atoms, is a potent inhibitor of muscle contraction. At which step in the contraction cycle would you expect /3, y-methylene-ATP to block contraction ... 

Beside thioamides, dithioesters are the most stable and accessible thiocarbonyl compounds. Their specific reactivity, in particular towards nucleophiUc reagents and their apphcations to the formation of carbon-carbon bonds, have already been reviewed [8]. However, as shown below, the presence of a phosphonate function alpha or beta to the thiocarbonyl group in phosphonodithioformates and phosphonodithioacetates makes these difunctional compounds very versatile building blocks. Moreover, for the phosphonodithioacetates, the substitution of the methylenic hydrogen atoms by fluorine increases again their potential as intermediates for the synthesis of modified natural and bioactive phosphorylated structures. 

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