
TY  - JOUR
A1  - Collins, DJ 
A1  - Downes, LM 
A1  - Jhingran, AG 
A1  - Rutschmann, SB 
A1  - Sharp, GJ 
T1  - Enolic Ortho Esters. I. Preparation and Birch Reduction of Some Coumarinoid Ortho Esters
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1989
VL  - 42
IS  - 8
SP  - 1235
EP  - 1248
KW  - 
UR  - https://doi.org/10.1071/CH9891235 
N2  - Phenolic ortho esters such as 4&#8242;,4&#8242;-dimethylspiro[2H-1-benzopyran-2,2&#8242;-[1,3]dioxolan] (7b) and 4&#8242;,4&#8242;-dimethyl-3,4-dihydrospiro[2H-1-benzopyran-2,2&#8242;-[1,3]dioxolan] (9c) were prepared in low yields by reaction of 2H-1-benzopyran-2-one (5) or 3,4-dihydro-2H-1-benzopyran-2-one (8a) with 2,2-dimethyloxiran in carbon tetrachloride in the presence of boron trifluoride etherate. 3,4-Dihydrospiro[2H-1-benzopyran-2,2&#8242;-[1,3] dioxoan ] (9a) and the corresponding 7-methoxy compound (9e) were obtained in high yield by reaction of (8a) or its 7-methoxy analogue (8b) with 1,2-bis(trimethylsily1oxy)ethane (10) in the presence of trimethylsilyl trifluoromethane-sulfonate . Birch reduction of phenolic ortho esters such as (9c) and (9e) afforded the enolic ortho esters 4&#8242;,4&#8242;-dimethyl-3,4,5,8-tetrahydrospiro[2H-1-benzopyran-2,2&#8242;-[1,3] dioxola n] (11a) and 7-methoxy-3,4,5,8-tetrahydrospiro[2H-1-benzopyran-2,2&#8242;-[1,3]dioxolan] (llc) in high yields. Birch reduction of 4&#8242;,4&#8242;,5&#8242;,5&#8242;-tetramethylspiro[2H-1-benzopyran-2,2&#8242;-[1,3]dioxolan] (7c) gave a 1 : 3 mixture of 4&#8242;,4&#8242;,5&#8242;,5&#8242;-tetramethyl-3,4-dihydrospiro[2H-1-benzopyran-2,2&#8242;-[l,3] dioxolan ] (9d) and the corresponding 3,4,5,8-tetrahydro compound (11b). Acid hydrolysis of the enolic ortho ester (11a) gave 67% of 2-hydroxy-2-methylpropyl 3-(2-oxocyclohex-3-enyl) propanoate (20). 
ER  -

