From 2- tetrahydropyrans

Cerkovnikov and Ustricev (1938) starting from tetrahydropyran-4-propionic acid (A R = CHj. CHj. COjH), which was converted by the Curtius-Schmidt method into 4-(2-aminoethyl)-tetrahydropyran (A R = (CH2)2NH2), and this with fuming hydrobromic acid at 100°... 

Piperidine derivatives and acyclic substances such as trihalogeno-alkanes and dihalogenoalkylamines may be used as starting materials. The piperidine derivatives are obtained mainly from pyridine compounds. Dihalogenoalkylamines and trihalogenoalkanes are prepared from tetrahydropyran derivatives, dialkoxy-substituted malonic esters, or alkane-tetracarboxylic esters. 

Acetate pyrolysis is illustrated by the synthesis of penta-1,4-diene (Expt 5.14) from 1,5-diacetoxypentane. This is prepared from 5-chloropentyl acetate which is conveniently obtained from tetrahydropyran by treatment with acetyl chloride this ring-opening reaction offers interesting comparison with the methods for the preparation of a, cu-dihalides discussed in Section 5.5.1, p. 555. 

A convenient two-step method for tetrahydropyran synthesis from tetrahydropyran-2-ones can be achieved by using a titanocene complex in the presence of a stoichiometric reducing agent, followed by treatment with Amberlyst 15 and triethylsilane <1998JOC2360>. 

The enol triflates derived from tetrahydropyran-2-ones undergo a cross-coupling with benzenethiols catalysed by Ni(0) that gives the 6-arylsulfanyl-3,4-dihydro-2//-pyrans, readily oxidised to the stable sulfoxides. The latter undergo facile conversion to the a-lithiated enol ethers <03S584>. 

A Nazarov cyclisation of l-(3,4-dihydro-2//-pyran-6-yl)-3-phenylpropenones affords cyclopenta[Z)]pyranones (Scheme 9) <03OL4931> and the conjugated ethoxytriene 7 derived from tetrahydropyran-2-one also yields a fused cyclopentenone <03JOC9728>. 

Bromo-5-chloropentane is easily prepared from tetrahydropyran according... 

Chloropentyl acetate is similarly obtained in 85% yield from tetrahydropyran,1039,1040 and 4-chloro-l-methylpentyl acetate in 77% yield from tetrahydro-2,5-dimethylfuran 1038 yields are said to be still higher if 2.2 g of ZnCl2 per mole of cyclic ether is used.206... 

This clearly excludes alkylating agents that yield acetals or other reactive functionalities. The use of alkylating agents such as chloromethyl methyl ether (CICH2OCH3) or chloromethyl benzyl ether (CICH2OCH2C6H5), which produce acetals similar to that from tetrahydropyran (Table 8.6, item 20), is also provided in Table 8.6 (item 21). 

Reaction of 2,4,6-trifluoro-l,3,5-triazine 55 with l-amino-8-naphthol-3,6-disulfonic acid provides l-(4, 6 -difluoro-r,3, 5 -triazyn-2 -yl)amino-8-naphthol-3,6-disulfonicacidm95 % yield [90], Substitution of fluorine atoms in fluorotriazine dye 148 with the alkoxides, generated from tetrahydropyran-2-methanol, a- and p-methylglucopyranoside, D-sorbitol, D-mannitol and D-glucose, has been found to lead to the corresponding conjugates 149 (Schane 62) [91],... 

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