Monosulfonate esters

Another method for achieving selective pinacol rearrangement involves synthesis of a glycol monosulfonate ester. These compounds rearrange under the influence of base. 

A comparison has been made" of various monoterpenoid rearrangements cataiysed by either zirconium phosphates or by zirconium organo-substituted phosphonates, and acid-catalysed rearrangements of a-trans- and /3-cis-3,4-epoxycaranes have been described." It has been observed" that on exposure to Li (OBu )3AlH, perhydro-naphthalene-l,4-diol monosulfonate ester (269) rearranges to the 11-oxatricyclo-[5.3.1.0.2,6]undecane derivative (270) (see Scheme 88). 

Pyrimido[5,4-6][ 1,4]oxazine-4,7-diones (175) can be transformed to 4-monosulfonic esters (176) by treatment with sulfonic acid chlorides (Equation (26)) <89MIP47293>. 

The Wharton fragmentation was used as a key step in an approach toward the total synthesis of xenicanes by H. Pfander et al. ° Two optically active substituted frans-cyclononenes were synthesized starting from (-)-Hajos-Parrish ketone. First, the bicyclic 1,3-diol was protected regioselectively on the less sterically hindered hydroxyl group with p-toluenesulfonyl chloride in quantitative yield. Next, the monosulfonate ester was exposed to dimsylsodium in DMSO, which is a strong base, to initiate the desired heterolytic fragmentation. 

Wijnberg, J. B. P. A., De Groot, A. Induced ionization in 1,4-diol monosulfonate esters and its application in the synthesis of natural... 

Use as a Base. Both 1,2- and 1,3-diol monosulfonate esters react with LiAHTj functioning initially as a base and subsequently in a reducing capacity (eqs 21 and 22). ... 

A fourth approach to the oxatricyclo-[5.3.1.0 ]-undecane ring system of furanether B (18.8) was published recently by de Groot et al. 159) who relied upon a stereoselective base-induced rearrangement reaction of 1,4-diol monosulfonate esters to establish the bridged ether core of 18.8 (26.103 26.105, Scheme 35). The starting material of the synthesis was the known ketone 26.99 which was converted to the required methanesulfonate 26.103 by standard procedures. 

A-Alkylimidazoles. Thionylimidazole has found great utility in the synthesis of A-alky limidazoles. Tertiary alcohols react with TDI to form monosulfonic ester imidazolides that rearrange to transfer the imidazole to the tertiary carbon (eq 7). The products are also obtained by treatment of the trityl chloride with imidazole however, comparison of the two procedures is not possible as yields were not reported. ... 

---