| 摘要 |
<p> <CHEM> where R1 is hydrogen, lower-alkyl, cyclo-alkyl-lower-alkyl, phenyl-lower-alkyl, lower-alkenyl or lower-alkynyl; three of R2, R2 min , R2 sec and R2''' are hydrogen and the fourth is hydroxy; R3 and R4 are each hydrogen or lower-alkyl, or R3 and R4 together are divalent lower-alkylene, -(CH2)m-, where m is one of the integers 3 and 4; n is one of the integers 2-4; X is oxygen or sulfur (-O- or -S-); and Alk is lower-alkyl, which comprises heating in an acid medium, a compound having the formula: <CHEM> where three of R2, R2 min , R2 sec and R2''' are hydrogen and the fourth is methoxymethoxy; R1, R3, R4, n, X and Alk have the meanings given above, and Alk min is lower-alkyl.</p> |
