Chiral cyclopropanes: asymmetric synthesis of constanolactones A and B

Solvolysis of allylic prostaglandin mesylates: moderate 1,3-syn-stereoselectivity

“…4, 5 An attractive possibility is to use the biomimetic rear rangement of the carbocations presented in Scheme 1 in the chemical synthesis, which would enable one to per form a short synthesis. 6 In addition to the very possibility of performing this rearrangement, an equally important problem is the stereoselectivity of the reaction center transfer.…”

Acetylenosaccharides

“…The pioneering work in additions to fully protected aldehydo-saccharides was by Horton and co-workers [105], a typical example being the addition of HCaCsMgBr to the isopropylidenated glyceraldehyde 64 to provide a 44:56 mixture of the propargylic alcohols 65a and 65b [106] (Scheme 5.14). The yield of the desired isomer may be increased by judicious choice of the reaction conditions, as illustrated by 184 the transformation of 66 into 67a and 67b in ratios ranging from 75:25 to 40:60 [107], by the transformation of the unwanted isomer into the desired isomer through a Mitsunobu reaction (see, for example [108][109][110][111]), or by oxidation of the epimeric alcohols to the ynone followed by reduction with Selectrides [112]. The propargylic amines 69a and 69b were obtained with excellent diastereoselectivity, albeit in low to moderate yields, by the addition of Me 3 SisCaCsLi to the aldimine 68 [113].…”

Synthesis of syn and anti 1,4‐Diols by Copper‐Catalyzed Boration of Allylic Epoxides

“…Most of the effort in this field has been focused on the synthesis of symmetrical 1,4-diols, [2] which can be difficult to apply to the total synthesis of complex molecules. Asymmetric reductions of chiral g-hydroxy ketones, [3] additions of 1-alkyn-3-ols to aldehydes, [4] and olefination reactions [5] are some of the most common ways to access enantiomerically pure nonsymmetrical 1,4-diols. Although good levels of diastereoselectivity can be achieved, two different chiral sources are generally needed to introduce the two oxygenated stereocenters, and their application to total synthesis can be problematic.…”