
TY  - JOUR
A1  - Aggarwal, Rachna 
A1  - Birkbeck, Anthony A. 
A1  - Giles, Robin G. F. 
A1  - Green, Ivan R. 
A1  - Gruchlik, Yolanta 
A1  - Oosthuizen, Francois J. 
T1  - Regioselectivity in the Syntheses of Enantiopure 2-Benzopyrans through Intramolecular Cyclization of Tethered Lactaldehydes. Conformations of the Products
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 2003
VL  - 56
IS  - 5
SP  - 489
EP  - 498
KW  - 
UR  - https://doi.org/10.1071/CH03027 
N2  - Using titanium tetraisopropoxide, the enantiopure tethered lactaldehyde (&#945;&#8242; S,2S)-2-(3&#8242;-hydroxy-&#945;&#8242;-methyl-benzyloxy)propanal (6) is cyclized with complete regio- and diastereoselectivity ortho to the phenolic hydroxyl group to give (1S,3S,4R)-3,4-dihydro-1,3-dimethyl-2-benzopyran-4,5-diol (7). Similar cyclization of the epimeric (&#945;&#8242; R,2S)-lactaldehyde (25) yields solely the corresponding (1R,3S,4R)-4,5-diol (34). The 4,5-diacetate (26), but not (35), undergoes conformational inversion of the heterocyclic ring through significant 4,5-peri interactions between the adjacent acetoxy substituents. Spontaneous cyclizations of the corresponding phenoxide ions of the lactalde-hydes (6) and (25), generated by fluoride from their silyl ethers, led to the related 4,7-diols with high regioselectivity through ring-closure para to the aromatic oxygen. 
ER  -

