Chiral sulfoxides in asymmetric synthesis: Enantioselective synthesis of (−)-(5S,7R)-Tarchonanthuslactone

An Efficient Asymmetric Synthesis of Tarchonanthuslactone

“…In order to regenerate the α,β‐unsaturated δ‐lactone moiety, the ester 11 was treated with pyridinium chlorochromate (PCC) in dichloromethane to provide lactone 12 in an acceptable yield of 66% and with a diastereomeric excess greater than 96%. Possible racemization could be ruled out, because all analytical data, including the optical rotation of TBS‐protected tarchonanthuslactone ( 12 ), corresponded to those reported by Solladié et al2d Finally, deprotection of the aromatic hydroxy groups according to Solladié et al by treatment of TBS‐protected tarchonanthuslactone ( 12 ) with tetrabutylammonium fluoride (TBAF) and benzoic acid in THF furnished the target molecule tarchonanthuslactone ( 1 ) in a good yield of 87% 2d. The synthesised title compound showed the same optical rotation ([α] D 28 = −80.8, c = 0.4, CHCl 3 ) and analytical data as the natural product isolated from nature by Bohlmann et al1 or as synthesized by Solladié and co‐workers 2d.…”

“…The secondary alcohol 2 was then directly treated with the doubly TBS‐protected acid 3 in the presence of dicyclohexylcarbodiimide (DCC) and 4‐(dimethylamino)pyridine (DMAP) without any further purification to yield ester 11 . Acid 3 had previously been synthesized starting from caffeic acid by hydrogenation and TBS‐protection by a literature method 2d. The yield of the reduction/esterification procedure was 72% and a diastereomeric excess of only 43% was determined by 13 C NMR analysis.…”

Synthesis of Homophthalates by [3+3] Cyclocondensation Reactions of 1,3-Bis(silyloxy)-1,3-butadienes with Silylated Methyl 3,5-Dioxohexanoate

“…Methyl 3,5-dioxohexanoate (2) was prepared by reaction of dehydracetic acid (1) with magnesium methanolate in 89 % yield (Scheme 1) [12]. Silylation of 2 resulted in the formation of silyl enol ether 3 (77 % yield) which exists as a mixture of three isomers which were not structurally assigned.…”

Synthetic Approaches to α,β‐Unsaturated δ‐Lactones and Lactols

“…[2] Accordingly, a number of inventive approaches have appeared in the literature in the last ten years. It is not intended to give an exhaustive account (more classical methods involving an ynoate triple bond reduction/lactonization sequence, [3] (Z)-selective olefinations, [4] nucleophile-induced isomerizations of (E)-α,β-unsaturated esters, [5] and selective oxidations of 1,5 diols [6][7][8][9][10] are not covered here) but rather to highlight recent advances in the field, particularly catalytic and asymmetric accesses. …”