Ring opening, diaxial

Treatment of benzyl 2-acetamido-3,4-anhydro-2-deoxy-6-C>-trityl-a-D-allopyranoside (412) with tetrabutylammonium fluoride [BU4NF in refluxing (refl.) MeCN, 24 h] gave, under diaxial ring-opening, benzyl 2-acetamido-2,4-dideoxy-4-fluoro-6-f9-trityl-a -D-gulopyranoside (413), in... 

With cyclohexene epoxides, the ring opening is frans-diaxial. 

In cyclic systems, ring opening gives the diaxial diol. 

It is not unlikely that the actual reagent is HOCl attack on the 9,11-olefin by Cl+ would occur from the less hindered side to give the 9a,lla-chloronium intermediate. Attack of OH to give diaxial ring opening would lead to the observed halohydrin. 

Working on modifications of trehalose, Richardson (with P.A. Monroe and Les Hough) demonstrated the selective tosylation at 0-2 of 4.6.4. 6 -di-(9-benzylidene-a,a-trehalose to afford a symmetrical 2,2 -ditosylate, which could be converted into the bis-manno-epoxide by the action of base (Scheme 24). The latter underwent trans-diaxial ring-opening with nucleophiles at C-3 and C-3, and many synthetic applications of this intermediate have now been recorded. One of these is shown in Scheme 24, from the Richardson-Hough laboratory, performed by postdoctoral fellow, Edward Tarelli, who contributed voluminously with Richardson to the exploration and development of trehalose chemistry. 

The frans-diaxial ring opening of 5(S.6(S-epoxvsteroids also gave the corresponding 5ot-chloro-6(3-hydroxy products (Scheme 24). 

The reaction of oxiranes with carbon nucleophiles provides a general method for the synthesis of B-type branched sugars. Thus, the diaxial ring-opening of methyl 2,3-anhydro-4,6-0-benzylidene-a-L-mannopy-... 

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