Methylene reactions with

Fig. 5. Alteration of end groups by reaction with methylene bases.

Fluonnated ylides have also been prepared in such a way that fluonne is incorporated at the carhon P to the carbamonic carbon Vanous fluoroalkyl iodides were heated with tnphenylphosphine in the absence of solvent to form the necessary phosphonium salts Direct deprotonation with butyUithium or hthium dusopropy-lamide did not lead to yhde formation, rather, deprotonation was accomparued by loss of fluonde ion Flowever deprotonation with hydrated potassium carbonate in thoxane was successful and resulted in fluoroolefin yields of45-S0% [59] (equation 54) P-Fluorinated ylides may also be prepared by the reaction of an isopropyli-denetnphenylphosphine yhde with a perfluoroalkanoyl anhydnde The intermediate acyl phosphonium salt can undergo further reaction with methylene tnphenylphosphorane and phenyUithium to form a new yhde, which can then be used in a Wittig olefination procedure [60] (equation 55) or can react with a nucleophile [6/j such as an acetyhde to form a fluonnated enyne [62] (equation 56)... 

Zinc-copper couple, 41, 72 reaction with methylene iodide and cyclohexene, 41, 73... 

Methylene bromide is essentially less effective in radical reactions as a chain transfer agent as a result, the reactions with methylene bromide proceed non-selectively and with small conversion of starting substrate. 

Cyclopropanation with Halomethylzinc Reagents. A very effective means for conversion of alkenes to cyclopropanes by transfer of a CH2 unit involves reaction with methylene iodide and a zinc-copper couple, referred to as the Simmons-Smith reagent.169 The reactive species is iodomethylzinc iodide.170 The transfer of methylene occurs stereospecifically. Free CH2 is not an intermediate. Entries 1 to 3 in Scheme 10.9 are typical examples. 

The phosphonic group can be introduced in position 4 of a pyran ring (66) by utilization of phosphorus-containing UN 67 in a reaction with methylene-active ketones 35 or 36 on continuous heating in ethanol (00PS(165)17) (Scheme 15). 

From Catechol. Several routes have recently been developed for the synthesis of heliotropin from catechol. In one such route, catechol is converted into 3,4-dihydroxymandelic acid with glyoxylic acid in an alkaline medium in the presence of aluminum oxide. 3,4-Dihydroxymandelic acid is oxidized to the corresponding keto acid (e.g. with copper-(II) oxide), which is decarboxylated to 3,4-dihydroxybenzaldehyde [176]. The latter product is converted into heliotropin, for example, by reaction with methylene chloride in the presence of quaternary ammonium salts [177]. 

The fact that functionalization of polymers and small molecules is observed to occur predominately on terminal (methyl) carbon atoms does not imply that the oxyfluorination reaction is truly selective. Although the reaction mechanism has not been studied in detail, it is undoubtedly a free-radical process. Molecular oxygen reacts spontaneously with the fluorocarbon—hydrogen radicals generated by fluorine during the fluorination process. Acid fluorides are retained on terminal carbon atoms because they are stable in 1 atm of elemental fluorine. Hypofluorites, which may be short-lived intermediates of oxygen reactions with methylene radical sites along the carbon chain, are not observed in the functionalized polymers. It is probable that, if they are intermediates, they are cleaved and removed by the excess elemental fluorine. 

Among other reactions of the hydrated electron may be mentioned the reaction with methylene blue. Methylene blue may be regarded as the prototype of easily reducible biological substances such as NAD, cytochrome-c, etc. The preliminary value for the rate constant for reaction with the hydrated electron (5) has now been shown to be too high, and the more reasonable value of 2.5 X 1010 M-1 sec.-1 has been obtained (19). It is thus no longer necessary to attribute special properties to methylene blue. 

Reaction with methylene iodide and an olefin see Simmons-Smith reaction. 

Improved sensitivity can be achieved by keeping the aqueous phase inside the chamber and adding the organic phase into it from the top the extracted analyte remains on the bottom and is then pushed forwards towards the detector. The feasibility of this approach was demonstrated by the determination of anionic surfactants in natural waters by reaction with methylene blue and extraction into chloroform [193]. The reported analytical figures of merit were very good. 

---