5- Bromo-6-methoxy-5,6-dihydro-27/-pyran

Hydroboration and oxidation of 3,4-dihydro-2-methoxy-2//-pyran gives a mixture of cis- and rra s-5-hydroxy-2-methoxytetrahydropyran (70CJC2334). After methylation, trans-2,5-dimethoxytetrahydropyran was isolated in small amounts. The cis isomer was obtained from 3,4-dihydro-3-methoxy-2//-pyran via 3-bromo-2,5-dimethoxytetrahydropyran. 

A new way to obtain Mo-coordinated parent 2/f-pyran (1) has been discovered in a multistep procedure starting from D-arabinose via optically pure tra/ii-5-bromo-6-methoxy-5,6-dihydro-2//-pyran, which gave (15)-tetrafluoroborate 138a by subsequent action of Mo(MeCN)3CO and other reagents. The corresponding (lf )-enantiomer 138b was obtained analo-... 

---