A Short and Efficient Synthesis of Crocetin-dimethylester and Crocetindial

Abstract

In this paper we describe an efficient six-step synthesis of crocetin-dimethylester that could be further reduced to a "four-step" synthesis through the use of in situ procedures. The simplicity of the whole process, the ready availability of starting materials, and the high overall yield render this strategy a very attractive synthesis of this very important compound, which is the key intermediate for the synthesis of several carotenoids and other polyene natural products.

Highly Enantioselective γ‐Amination by N‐Heterocyclic Carbene Catalyzed [4+2] Annulation of Oxidized Enals and Azodicarboxylates

“…The addition of in situ generated NHC to enals gives the vinyl Breslow intermediate A, which decomposes to the azolium dienol B by removal of the g leaving group. The readily available substrates, [19] broad reaction scope, excellent enantioselectivity, and mild reaction conditions [20] make this g-amination process potentially useful for the synthesis of g-amino acids and their derivatives. In summary, the NHC-catalyzed [4+2] annulation of enals, having a g leaving group, and azodicarboxylates was developed, thus giving the corresponding dihydropyridazinones in good yields with excellent enantioselectivities.…”

Total Synthesis of (±)‐Symbioimine

“…Continuing with the synthesis, 7 was converted into the iodide 8 in two steps by mesylation (98 %) and S N 2 substitution by using NaI in acetone (93 %). Transmetalation of 8 with t BuLi at −80 °C followed by trapping of the organolithium intermediate with the known (2 E )‐4,4‐dimethoxybut‐2‐enal16 9 , successfully afforded aldehydes 12 after protection of the hydroxy group with a silicon protecting group followed by hydrolysis of the acetal. Thus, syntheses of all‐ E ‐undeca‐2,8,10‐trienals 12 with TBDPS, TIPS, and TBS protecting groups were possible.…”

Total synthesis of (3S, 5R, 3'S, 5'R)-capsorubin

“…20 More recently, we have also described a short, efficient synthetic route for the preparation of crocetindial (3) using two in situ procedures: a ketal hydrolysis/Wittig reaction and an allylic oxidation/Wittig reaction. 21 In this paper we describe an alternative asymmetric route to the enantiomerically enriched compound 2a. The total synthesis of (3S, 5R, 3'S, 5'R)-capsorubin (1) was achieved by a new experimental procedure involving the condensation of compounds 2a and 3.…”

“…21 Optically active capsorubin (1) was finally obtained by a new experimental procedure involving the condensation of compounds 2a and 3, using LDA as base, as depicted in Scheme 2. Under this condition, compound 1 was obtained in 43% yield after purification by recrystallization.…”