Tetrahydrofuranyl ester

Ph2CHC02-2-tetrahydrofuranyl, 1% TsOH, CCI4, 20°, 30 min, 90-99% yield. The authors report that formation of the THF ether by reaction with 2-chlorotetrahydrofuran avoids a laborious proce ure that is required when dihydrofuran is used. In addition, the use of dihydrofuran to protect the 2 -OH of a nucleotide gives low yields (24-42%)." The tetrahydrofuranyl ester is reported to be a readily available, stable solid. A tetrahydrofuranyl ether can be cleaved in the presence of a THP ether. ... 

Tetrahydrofuranyl Ester RC02-2-tetrahydrofuranyl Formation/Cleavage ... 

Compared to the well-known OBO esters [81], the ABO esters are more stable towards protic acids but less stable towards the Lewis acid Cp2ZrCl2/AgC104, which isomerizes the ABO orthoester to a tetrahydrofuranyl ester. Selective deprotection is therefore possible (Scheme 8.41). 

Baldwin s rules work because they are based on whether or not orbital overlap can be readily achieved in the conformation required at the transition state. You met in the last chapter the principle of microscopic reversibility, which says that, if a reaction goes via a certain mechanism, the reverse reaction must follow exactly the same path in the opposite direction. So Baldwin s rules also work for ring-opening reactions. This is where the unfavourability of 5-endo-trig really is important this tetrahydrofuranyl ester, for example, looks set up to do an El cB elimination in base. Indeed, when it is treated with methoxide in deuterated methanol it exchanges the proton a to the ester for deuterium, proving that the enolate forms. But is does not eliminate elimination would be a reverse 5-endo- frig process and is disfavoured. 

The catalytic oxidative carbonylation of allene with PdCb and CuCh in MeOH affords methyl a-methoxymethacrylate (559)[499]. The intramolecular oxidative aminocarbonylation of the 6-aminoallene 560 affords the unsaturated J-amino ester 561. The reaction has been applied to the enantioselective synthesis of pumiliotoxin (562)[500]. A similar intramolecular oxycarbonyla-tion of 6-hydroxyallenes affords 2-(2-tetrahydrofuranyl)acrylates[501]. 

Scheme 1. Malic ester-derived synthesis of bis-tetrahydrofuranyl alcohol 11...

A double Michael addition on the trihydroxydienoate 5 leads to the bicyclic ester 6 with total stereoselectivity. After protection of the primary hydroxy function, the dienoate is treated at 20 C with potassium /cr/-butoxide in a mixture of ten-butyl alcohol/benzene. The desired bicyclic ester 6, containing both tetrahydrofuranyl and tetrahydro-2/f-pyrany] moieties, is obtained in about 50% yield. This compound is stereochemically pure and its structure is confirmed on the basis of the H-NMR spectrum51. 

The tandem Homer-Wadsworth-Emmons and Michael reactions have been applied to lactols, providing tetrahydropyranyl or tetrahydrofuranyl derivatives to the hemiaminal derived from A-Boc-protected pyroglutamic esters, providing 5-substituted prolinates and to imidate anion, providing oxazolidine. On reaction with lactols, replacement of the cyanomethylphosphonate by the 1-cyano-1-dimethylaminomethylphosphonate leads to the formation of a-cyano enamines as a... 

The reactions of ozone with simple tetrahydropyranyl ethers and conforma-tionally rigid p-glycosides were indeed discovered to give the corresponding hydroxy Z-esters exclusively under kinetically controlled conditions lactone formation was not observed [8-10]. For instance, p-D-glucopyranoside 131 reacted under acetylating conditions to form 132 exclusively, Eq. 33. The reactions of the tetrahydrofuranyl ethers 133, Eq. 34, and 135, Eq. 36, were similar to that of 131 only the esters 134 and 136 were obtained, respectively. 

The radical reduction of ester-substituted alkyl iodides bearing a chiral tetrahydrofuranyl substituent proceeds with high selectivities1522. A bulky group in the 4-position of the tetra-hydrofuran ring has little influence on the diastereomeric excess, whereas an alkoxy substituent in the 3-position increases the synjanti ratio. 

Tetrahydrofuranyl ethers (4) are also smoothly oxidized to 7-hydroxy esters... 

Full details have been disclosed of the synthesis of 2-tetrahydrofuranyl (THF) ethers (57) (Scheme 30) from either 2-chlorotetrahydrofuran (basic conditions) or the stable, solid, acetal ester (58) (acidic conditions). THF ethers are more basic... 

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