Stereoselective total synthesis of the acetylenic carotenoids alloxanthin and triophaxanthin.

Stereoselective total synthesis of the C(40)-diacetylenic carotenoid alloxanthin (1) and the C(31)-acetylenic apocarotenoid triophaxanthin (2) was accomplished by Wittig condensation of C(10)-dialdehyde 20 or C(16)-keto aldehyde 19, respectively, with C(15)-acetylenic tri-n-butylphosphonium salt 12.

Carotenoids and related polyenes, part 12. First total synthesis and absolute configuration of 3'-deoxycapsanthin and 3,4-didehydroxy-3'-deoxycapsanthin.

The synthesis of 3'-deoxycapsanthin (1) and 3,4-didehydroxy-3'-deoxycapsanthin (2), carotenoids of paprika, has been achieved by employing Lewis acid-promoted regio- and stereoselective rearrangement of the C(15)-epoxy dienal 5a. The absolute stereochemistry of the newly formed C-5 chiral center of rearrangement product 6a was determined to be (R) from its alternative synthesis derived from (+)-(R)-camphonanic acid (11).

Stereocontrolled first total syntheses of amarouciaxanthin A and B.

The first total syntheses of amarouciaxanthin A and B (C40) via the stereoselective Wittig reaction of C15-allenic and C15-acetylenic tri-n-butylphosphonium salts with the unprecedented C25-3,8-dihydroxy-5,6-epoxyapocarotenal have been completed. Oxidation of the two hydroxyl groups in the left part of the resulting condensation products followed by regioselective oxirane ring opening gave the target carotenoids.