O-Benzylidene Tartaric Acid Derivatives

When either L-tartaric acid esters la,b or D-tartaric esters 2a,b are treated with benzaldehyde under acidic catalysis with Deair-Stark removal of generated water, good to excellent yields of either (4i ,5i )-(330) or (45, 5 S)-2-phenyl-l,3-dioxolane-4,5-dicarboxylates (331) are obtained [115,116]. Acetal exchange, which involves reaction of the tartaric diesters with benzaldehyde dimethyl acetal in the presence of an acid catalyst, is also an excellent protection method [117]. 

The versatile enantiomerically pure (25, 35)-4,5-dimethyl-2-phenyl-l,3-dioxolane (343) can be prepared on an economically large scale from L-tartaric acid in five steps in 63-68% 

Cyclic PAF analogues, such as the chiral tetrahydropyrans 361 and 363, represent con-formationally restricted glycerol derivatives that exhibit potent PAF antagonistic activity [126]. A twelve-step sequence converts 349 or 353 to (2i ,3 S)-(360) (ee = 98.8%) or (2S,3R)-2-triphenylmethoxymethyltetrahydropyran-3-ol (362) ( = 96.8%), respectively. These are then appropriately transformed to the corresponding PAF products 361 and 363 [127]. 

The design of PAF analogues with selective hypotensive activity but limited ability to cause platelet activation has resulted in development of a highly selective agonist (365) with orally-potential antihypertensive activity. The key feature in the synthesis of this agonist is 

The indolizidine alkaloid (+ )-monomorine I (373), isolated from Pharaoh s ant Mono-morium pharaonis, is the first example of an indolizidine alkaloid found in the animal kingdom. One enantioselective total synthesis of 373 exploits an asymmetric cycloaddition of nitrone 370 to the chiral allylic ether 369, which is prepared from 349. The conversion of 349 to a tosylate followed by treatment with -propylmagnesium bromide in the presence of 

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