Difluoromethylene group, from

This method can also be utilized as a general method for the preparation of olefins with terminal difluoromethylene groups from aldehydes.8 Also, by the substitution of tributylphosphine for triphenylphosphine in this procedure, ketones other than those containing an a-perfluoroalkyl group can be converted to terminal difluoromethylene compounds.9... 

Dexivacaine, 95 DBxnorgBstrel acetime, 152 Diabetes, 116 Diamocaine, 336 Diapamide, 93 Diaveridine, 302 Diazepam, 452 Diazoxide, 395 Dibenzepin, 424, 471 DichloroisopTTOterenol, 106 Diclofenac, 70 Dicyanamide, 21 Dieckmann cyclization, 72 Difenoximide, 331 Difenoxin, 331 Diflucortolone, 192 Diflumidone, 98 Diflunisal, 85, 86 Difluoromethylene groups, from ketones, 196 Difluprednate, 191 Dihydrocodeinone, 318 Dihydropyridine synthesis, 283... 

Miller et al. [9] hypothesized rules on the regioselectivity of addition from the study of the base-catalyzed addition of alcohols to chlorotnfluoroethylene. Attack occurs at the vinylic carbon with most fluorines. Thus, isomers of dichloro-hexafl uorobutene react with methanol and phenol to give the corresponding saturated and vinylic ethers The nucleophiles exclusively attack position 3 of 1,1-dichloro-l,2,3,4,4,4-hexafluoro-2-butene and position I of 4,4-dichloro-l,l,2,3,3,4-hexafluoro-1-butene [10]. In I, l-dichloro-2,3,3,4,4,4-hexafluoro-l-butene, attack on position 2 is favored [J/] (equation 5) Terminal fluoroolefms are almost invariably attacked at tbe difluoromethylene group, as illustrated by the reaction of sodium methoxide with perfluoro-1-heptene in methanol [/2J (equation 6). 

Sugars having a difluoromethylene group were prepared by reaction of an aldehyde group in sugars with difluoromethylene tris(dimethyl-amino)phosphorane some of these were 554- 559. Similarly, (Z)- 560) and f ))-. tw-bromofluoroalkene 561 were prepared from l,2 3,4-di-0-iso-propylidene-a-D-gfl/ac/o-hexodialdo-l,5-pyranose (395) by treatment with Ph3P=CFBr. 

Starting from Difluorovinyl Glycosides Saccharidic derivatives that have a difluoromethylene group in the pseudo-anomeric position are important synthetic intermediates for preparation of difluoro-C-glycosides, difluoro-C-phos-phonates, and difluoro-C-disaccharides. ° ... 

The double bond in l,4-dibromohexafluoro-2-butene surrounded by fluorines and difluoromethylene groups is prone to undergo a nucleophilic addition of ethanol. From the addition product, hydrogen bromide is eliminated in the alkaline medium by E2 mechanism, and the compound C6H5BrF60 is formed. Another explanation of the reaction is addition of ethoxide anion followed by elimination of bromide anion [76],... 

Functional groups containing the C = N bond, such as hydrazones, oximes and diazo compounds, can also be used in the synthesis of fluorinated derivatives and these reactions are the subject of this section. The reaction products in these procedures are usually the corresponding g cw-difluoromethylene compounds. Since oximes and hydrazones arc obtained from aldehydes and ketones, these reactions can be considered as an alternative to the direct transformation of a carbonyl group into the difluoromethylene group. As indicated in Section... 

The polymers formed from symmetric monomer units, such as polyethylene, (CH2CH2) and polytetrafluoroethylene, (CF2CF2) are an exception to this notation. Although the simplest repeat units are the —CHj— and —CF2— groups, we show two methylene groups and two difluoromethylene groups because they originate from ethylene (CH2= H2) and tetrafluoroethylene (CF2= F2), the monomer units from which these polymers are derived. 

The HF-pyridine reagent is an effective complement to di-methylaminosulfur trifluoride (DAST) reagent6 in the preparation of alkyl fluorides from alcohols. DAST is also useful for the conversion of carbonyl groups to difluoromethylene functions. The... 

The mechanism for the cyclization of these perfluoro ketones, proposed by German and coworkers5 and discussed in the review by Krcspan and Petrov.4 involves initial activation of the carbonyl with antimony V) fluoride and a 1.4-fluorine shift from the /1-trifluoromethyl group. The resultant difluoromethylene carbocation then cyclizes with the carbonyl oxygen to give the tetrahydrofuran. 

---