No abstract

An efficient and practical method for the synthesis of (4R,5R)-4,5-O-isopropylidene-cyclopent-2-enone was developed from D-ribose by using a ring-closing metathesis reaction.

A new approach is described for the asymmetric synthesis of 1-substituted 1,2,3,4-tetrahydroisoquinolines that is based on the enantioselective 1,3-dipolar cycloaddition reaction of a nitrone and a vinyl ether in the presence of a chiral phosphoric acid that gives the chiral tetrahydroisoquinolines in high yields and with high enantioselectivities. 1H and 31P NMR analyses of the mixture of nitrone and chiral phosphoric acid suggest the formation of a 1:1 complex.

The total synthesis of haliclonin A was accomplished. Starting from 3,5‐dimethoxybenzoic acid, a functionalized cyclohexanone fused to a 17‐membered ring was prepared through a Birch reduction/alkylation sequence, ring‐closing metathesis, intramolecular cyclopropanation, and stereoselective 1,4‐addition of an organocopper reagent to an enone moiety. Reductive C−N bond formation via an N,O‐acetal forged the 3‐azabicyclo[3.3.1]nonane core. The allyl alcohol moiety was constructed by a sequence involving stereoselective α‐selenylation of an aldehyde via an enamine, syn‐elimination of a selenoxide, and allylation of the aldehyde with an allylboronate. Formation of the 15‐membered ring containing a skipped diene was achieved by ring‐closing metathesis, and final transformations led to the synthesis of haliclonin A.