The hydrogenolysis of enantioenriched donor–acceptor (D–A) cyclopropanes using H2 (1 atm) and a catalytic amount of palladium on charcoal gave trans‐α‐alkoxycarbonyl‐β‐benzyl‐γ‐lactones or β‐substituted γ‐aryl‐α,α‐diesters with high enantiomeric excess. The reaction was also used as a key step in the asymmetric total synthesis of yatein with high ee and excellent dr. This demonstrates the utility of this new protocol for the asymmetric synthesis of trans‐α,β‐disubstituted γ‐butyrolactones. D–A cyclopropanes containing electron‐withdrawing groups at the β‐position were not susceptible to hydrogenolysis under these conditions. The reductive ring‐opening of a D–A cyclopropane using D2 instead of H2 generated the corresponding monodeuterated product.

Lewis acid-mediated ring-opening cyclization of trans-and cis-cyclopropanes 1a and 1b afforded the same trans-dihydronaphthalene 2a. Moreover, Lewis acid-mediated cyclization of 7R-and 7S-benzyloxy dibenzyl lignan lactones 5a and 5b furnished trans-tetralin 6a with high diastereomeric and enantiomeric excess. Based on these results, we rationalized the mechanisms of the cyclizations via trans-selective intramolecular FriedelCrafts alkylation/cyclization, via the S N 1 pathway.Keywords: Ring-opening cyclization | Cyclopropane | Friedel-Crafts reactionCyclization reactions of donoracceptor (DA) cyclopropanes are recognized as versatile protocols for the syntheses of carbocyclic and heterocyclic scaffolds.1,2 As part of a program of synthetic studies using cyclopropropane moieties, 3,4 we achieved the first asymmetric total synthesis of (+)-podophillic aldehydes using the highly stereoselective Lewis acid-mediated ring-opening cyclization of DA cyclopropylcarbinols to afford 1-aryl-1,2-dihydronaphthalene with retention of stereochemistry and high enantiomeric excess (Scheme 1). 4fRecentry, France and co-workers improved our method by using a catalytic amount of Ca(NTf 2 ) 2 instead of a stoichiometric amount of BF 3 ¢OEt 2 or Sc(OTf ) 3 .5 Although the modified method can provide a variety of cyclic compounds, this method deals with racemic substrates. Meanwhile, the mechanism of the reaction has not been revealed, and two plausible mechanisms can be proposed. One is the FriedelCrafts-type attack of the aromatic ring to the benzyl cation to furnish the trans-product based on the neighboring chiral center (trans-selective S N 1 pathway via cation A). The other is the pericyclic reaction-like 6 mechanism via transition state B with retention of stereochemistry of the cyclopropane. In France's report, a substrate bearing cyclic cis-2,3-disubstituents was employed to investigate the diastereoselectivity and it afforded the cis-substituted tetracyclic product (Scheme 2). This result seems to support the pericyclic reaction-like mechanism. However, a cyclic cation can prevent the construction of the tetracyclic trans-cyclopentene product due to the high strain (on the basis of our calculation using Spartan 09 using B3LYP/6-31G(d), the energy of cis-product is 6.6 kcal mol ¹1 lower than that of trans-product). Here, we report the diastereoselectivities of the ring-opening cyclization of trans-and cis-cyclopropanes 1a and 1b along with similar cyclizations of 7-benzyloxy dibenzyl lignan lactones 4a and 4b. Based on those results, we elucidate the reaction mechanism.Investigation of the diastereoselectivities of the ringopening cyclizations of 1a and 1b is key to reveal the reaction mechanism (Scheme 3). Following our previously reported transformation 4a of dichlorocyclopropane, the desired substrates 1a and 1b were obtained in good yields. However, cyclopropanations of (E)-and (Z)-1-phenyl-1-propenes using α,α-diazo-β-ketoester in the presence of the Rh 2 (esp) 2

The total synthesis of four lignans including (−)- and (+)-niranthin has been achieved utilizing cyclopropanes. Based on bioassays of the (+)- and (−)-niranthins using HBV and IFV, we speculated the bioactive site of niranthin against HBV and IFV.