The synthesis of a focussed library of sphingolipids differing in the number and position of 13C labels is described. The synthesised sphingolipids differ in substitution at both the sphingosine amine (either palmitoylated or unmodified) and the sphingosine primary hydroxyl (unmodified or glycosylated). Moreover, 13C atoms are incorporated into either the sphingosine or the palmitate moiety, or both. This set of compounds is intended for use in relative quantitative lipidomics studies to gain insight into sphingolipid metabolism in healthy and diseased (lysosomal storage disorders) patients and animal models.

An enantioselective synthesis of an intermediate in the Tanino total synthesis of solanoeclepin A has been developed. The key step was an intramolecular [2+2] photocycloaddition, which led to the tricyclo[5.2.1.0(1, 6)] decane core in six steps. The first photosubstrate, prepared through an indium-mediated Barbier-type reaction, gave an excellent [2+2] cycloaddition, but it could not be obtained in sufficient enantiopurity. The second photosubstrate, prepared through an asymmetric allene diborylation in high enantiomeric excess, gave the [2+2] cycloaddition product in high yield on irradiation at 365 nm on 20 g scale in a flow system. Other important steps were the replacement of a boronate group at the quaternary carbon by a vinyl group and diastereoselective cyclopropanation of an allylic alcohol.

The [2+2] photocycloaddition of allenes 15-18, 23 and 26 was studied. Irradiation of a solution of these substrates in acetonitrile at 300 nm resulted in the clean conversion of the starting materials into a mixture of photoproducts. The major product in all cases was a bicyclic pyrrole or furan fused to an eight membered ring (43-70 % yield). The formation of these products is thought to be a result of a heteroatom-induced fragmentation of the straight adduct (7). This is supported by irradiation of the carbon analogue 32 which al-

This report describes intramolecular [2+2] photocycloadditions of several butenolides with an allenylmethyl substituent at the 5-position. These photosubstrates were prepared from 2-(silyloxy)furans through silver-mediated reactions with allenylmethyl bromides. Two cases were studied where the lactone was replaced by an N-Boc-lactam. Irradiations of the photosubstrates were carried out with 300 nm UV-light in acetonitrile/acetone mixtures. Crossed cycloadducts were produced in good yields via cycloaddition of the heterocyclic double bond with the allene internal double bond. The products were γ-lactones (γ-lactams) containing the strained 5-methylenebicyclo[2.1.1]hexane skeleton. In some cases the

An enantioselective synthesis of the right‐hand substructure of solanoeclepin A has been developed. The key step was an intramolecular [2+2] photocycloaddition between an allene and a butenolide providing a methylenecyclobutane with three quaternary carbon atoms in a complex tetracyclic framework. Other crucial steps included an enantioselective Noyori transfer hydrogenation of a ketone, a diastereoselective silver‐mediated silyl dienolate allylation, and a diastereoselective cyclopropanation of an allylic alcohol. The installation of the bridgehead methyl group by reduction of the lactone moiety proved to be troublesome.