Carbocyclic serine analogues: regio- and diastereoselective syntheses of new 1-amino-2,5-dihydroxycyclohexanecarboxylic acids

Spirooxazolones 3, obtained by Diels–Alder reaction between oxazolone 1 and dienes 2, are the key starting materials for the preparation of β-hydroxycyclohexenamino acid derivatives 4–6. The regio- and diastereoselective functionalization of cyclohexyl ring with a second hydroxy group to give the new 1-amino-2,5-dihydroxycyclohexanecarboxylic acids 11, 19 and the 2,4-dihydroxy derivative 20 was achieved when starting from compounds 4–6. In fact, the iodo-oxazination reaction on compounds 4, followed by reduction of the iodine atom, led to the dihydroxyamino acids 11 in which the cis relationship exists between the two hydroxy groups. The iodo-lactonization reaction, followed by reduction of the iodine atom, allowed for the formation of the trans dihydroxy derivatives 19 starting from the acids 5.