Tetrahydropyranyl ethers rearrangement

A solution of the ester (56) and the tetrahydropyranyl ether (57) was irradiated to form the intermediate compound (58), which would rearrange through a retro-aldol reaction and a hemiacetal formation route to the less strained six-membered heterocycle (59). The hemiacetal (59) could be converted to loganin (55) in several steps Z3>. 

A 1,2-hydride shift has been invoked399 to account for the formation of p-methoxyphenylbutyraldehyde derivatives (337) during the treatment of />methoxy-benzyl-protected allylic alcohols (336) with zeolites. A similar C-glycosidation procedure involving Lewis acid-catalysed anomeric oxygen to carbon rearrangement of tetrahydropyranyl ether derivatives has been reported400 (see Scheme 82). It has been... 

Treatment of alkynyl tri- -butyltin tetrahydropyranyl ether derivatives with BF3-OEt2 effects an anomeric oxygen to carbon rearrangement, furnishing the corresponding carbon-linked alkynol products (Equation (64)).218... 

The rearrangement which involves the intermediacy of the same cyclopropylcarbinyl cation (138) is completed in few minutes as monitored by t.l.c. Upon treatment with 10 mol % of pyridinium p-toluenesulphonate (PPTS) in ethanol at 55°C in order to cleave the protective group, some tetrahydropyranyl ethers of conjugated dienols (140) or enones (141) have undergone total C3 - C4 ring enlargement (equation 102) ... 

Of interest is the rearrangement of 3-tributylstannylprop-2-ynyl tetrahydropyranyl ethers to 3-tetrahydropyranylpropynols. ... 

In 1975, van der Baan and Bickelhaupt reported the synthesis of imide 37 from pyridone 34 as an approach to the hetisine alkaloids, using an intramolecular alkylation as the key step (Scheme 1.3) [23]. Beginning with pyridone 34, alkylation with sodium hydride/allyl bromide followed by a thermal [3,3] Claisen rearrangement gave alkene 35. Next, formation of the bromohydrin with A -bi omosuccinimide and subsequent protection of the resulting alcohol as the tetrahydropyranyl (THP) ether produced bromide 36, which was then cyclized in an intramolecular fashion to give tricylic 37. 

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