Hydroxylactones cyclic

The cyclic a-hydroxylactone, pantolactone, has been used extensively as a chiral auxiliary in D-A reactions.84 Reactions involving TiCl4 and SnCl4 occur through chelated TSs.85... 

It is not necessary to have an all-carbon ring to preserve the cis geometry of a double bond. Lactones (cyclic esters) and cyclic anhydrides are useful too. A double bond in a five- or six-member ed compound must have a cis configuration and compounds like these are readily made. Dehydration of this hydroxylactone can give only a cis double bond and ring-opening with a nucleophile (alcohol, hydroxide, amine) gives an open-chain compound also with a cis double bond. The next section starts with an anhydride example. 

Unpublished experiments indicate that 5-formyl-4-phenan-throic acid exists mainly in the cyclic hydroxylactone form. 

We shall illustrate this with Prestwich s synthesis11 of the natural anti-cancer compound (—)-aplysistatin 69. This interesting compound with a seven-membered cyclic ether and a bromine atom proclaiming its marine origin is probably made in nature by a polyolefin cyclisation and that strategy was used in the synthesis. The alkene must be removed 70 before the cyclisation can be reversed. The stereochemistry of the extra centre in 70 is unimportant until the realisation that it can be made by alkylation of a hydroxylactone 71 whose stereochemistry must be anti. 

In 1974, Porra and Grimme (8) extracted Chls aerobically from "recalcitrant" Chlorella fusca cells, with 2.1M pyridine in 0.35M NaOH. The Chls were oxidized to and measured as their allomerization products, Mg-cyclic hydroxylactones a and b (Fig. 2 V). Recently, a... 

Yellow cryst. (chlorobenzene). Mp 262-263°. Tautomerises to cyclic hydroxylactone. 

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