4.6.6- Trimethyl-1,3-oxathiane

Chiral tertiary u-hydroxy aldehydes This chiral 1,3-oxathiane (1) undergoes the highly selective reactions shown by 4,4,6-trimethyl-1,3-oxathiane (this volume) to give the optieally aetive oxathiane carbinols 3 in greater than 90% diastereomeric purity. These are cleaved by NCS antj silver nitrate (4, 216) to a-hydroxy aldehydes (4) and a sultine. which can be converted back to 1 (95% yield). The a-hydroxy aldehydes (4) are unstable... 

The semi-empirical theoretical study (AMI, PM3, and force field) of 2,2,5-trimethyl- 2,2-dimethyl-5- o-propyl-, and 5- T7-butyl-2,2-dimethyl-l,3-oxathiane 47-49 afforded the correct conformational equilibria as obtained by FI NMR spectroscopic conformational analysis <2001RJC1487>. The chair conformation is adopted while the substituent at position 5 is in an equatorial position. Furthermore, there was no indication for the presence of twist conformers. 

CHIRAL 1,3-OXATHIANE FROM (+)-PULEGONE HEXAHYDRO-4,4,7-TRItCTHYL-4H-l, 3-BEN 2DXATHIIN (4H-1,3-Benzoxathiin, hexahydro-4,4,7-trimethyl-)... 

Hexahydro-4,4,7-trimethyl-4H-l,3-benzothiiii (1). The optically pure 1 can be prepared from ( + )-pulegone in about 30% yield. The isomer 2, in which the oxathiane group is enantiomeric to that in 1, is obtained as a by-product. 

Stereoselective synthesis of oxathiane tertiary carbinols (8, 508-509). This reagent is now preferred over the isomeric 4,6,6-trimethyl- 1,3-oxathiane (8, 508-509) for a two-step, highly stereoselective synthesis of oxathiane tertiary carbinols (3, equation I), which can be cleaved to enantiomerically pure tertiary a-hydroxy aldehydes. The first step, acylation with retention of configuration, gives the more stable equatorial adduct 2... 

Diastereospecific reaction of a Grignard reagent. This reagent has been used as the chiral adjunct in place of 4,6,6-trimethyl-l,3-oxathiane (8, 508-509) in a synthesis of atrolactic acid methyl ether (6) in 97 2% enantiomeric excess... 

Chiral 1,3-Oxathiane from (+)-Pu1egone [Hexahydro-4,4,7-trimethyl-4H-1,3-benzoxathi1n]... 

CgHi202Se, 2,4,6-Trimethyl-1,3,5-dioxaselenan, 39B, 285 C6H12O3S, 1,1,3-Trimethyltrimethylene sulfite, 44B, 374 CsH12O4S, (2R,4S,6S)-2-Hydroxymethyl-6-methoxy-1,4-oxathian S-oxide, 37B, 215... 

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