THF formation

Since 1,4-butanediol (BD) undergoes dehydration side reaction in the presence of acid resulting in THF formation, the hydroxy-ester interchange reaction is the preferred method for the preparation of PBT. The first stage of reaction is carried out at 150-200°C and consists of a hydroxy-ester interchange between DMT and excess butanediol with elimination of methanol. In the second stage, temperature is raised to 250°C and BD excess is eliminated under vacuum. Tetraisopropoxy-and tetrabutoxytitanium are efficient catalysts for bodi stages (Scheme 2.20). 

Finally stoichiometric addition of DIBAH in a nonpolar solvent at low temperature yields the desired aldehyde 11. Overreduction to the corresponding alcohol 33 is prevented under these conditions because of the formation of the relative stable intermediate 34, which decomposes only in the course of aqueous work-up. At higher temperature and in polar solvents such as THF formation of alcohol 33 occurs. Thus, grade of reduction of esters with DIBAH can be controlled by temperature and solvent. 

It has been demonstrated that optically active oxetanes can be formed from oxazolidinone 92, a crotonic acid moiety functionalized with Evans chiral auxiliary (Scheme 18) <1997JOC5048>. In this two-step aldol-cyclization sequence, the use of 92 in a deconjugative aldol reaction, with boron enolates and ethanal, led to formation of the syn-aldol 93. This product was then converted to the corresponding oxetanes, 94a and 94b, via a cyclization with iodine and sodium hydrogencarbonate. This reaction sequence was explored with other aldehydes to yield optically active oxetanes in similar yields. Unlike previous experiments using the methyl ester of crotonic acid, in an analogous reaction sequence rather than the oxazolidinone, there was no competing THF formation. 

Thankfully, as the quote points out, formate is not just floating around in solution. It is first attached to a vitamin called THF, a cousin of the B vitamin folic acid (don t even ask how the vitamin is synthesized). When it is attached by an enzyme to the vitamin (in a reaction requiring an energy pellet of ATP), formate is revved up and made ready for action. The THF-formate complex, however, would not join up with Intermediate IV to give Intermediate V unless directed to do so by Enzyme IV it would float away in the cell until it reacted with something else or decayed, and that would mess up our synthesis of AMP. That doesn t happen, however, because the enzyme guides the reaction to the correct products. 

Alkyl di-Grignard reagents can be reacted selectively with aliphatic and aromatic acid chlorides in the presence of tris(acetylacetonate)iron(III) [83]. The best conditions utilized alkyl chlorides in THF. Formation of alcohols is avoided in this one-step catalyzed... 

The aim of the present work is to elucidate the role of Co-Zn/porcelain catalyst support in 1,4-BD conversion and the natme of active Si02 (the main component of the support) surface sites needed for 2,3-DHF and tetrahydrofinan (THF) formation as well as the possible intermediates. 

Whether the oxetane or the tetrahydrofuran is formed depends on which end of the iodonium ion is attacked by the OH group. In terms of Baldwin s rules, oxetane formation is a simple A-exo-tet reaction and is favoured. The THF formation is sUghtly more complicated. It is a 5-exo-tet as far as the Sn2 reaction is concerned, but in the transition state the nucleophile, the carbon atom under attack and the leaving group are also all in the same six-membered ring—there is disfavoured 6-endo-tet character. It is very difficult... 

Figure 5.3 THF formation during synthesis of PBT (a) Intramolecular dehydration of BD and (b) Intramolecular elimination of hydroxybutyl ester end groups.

Lee, G.W.J. and Tadros, ThF., Formation and stability of emulsions produced by dilution of emulsifiable concentrated. Part I An investigation of the dispersion on dilution of emulsifiable concentrates containing cationic and non-ionic surfactants. Colloids Surf., 1982, 5,105—115. 

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