Ring-closing metathesis has been applied to a series of glucose derivatives to produce cyclopentene derivatives 5a and 5b, cyclohexene derivatives 8 and 9, cycloheptene 12, and cyclooctene 14. Spirocyclic dihydrofurans 19, 26a, and 26b, along with dihydropyran 22, were also produced. A range of fused oxepine derivatives 29a-c and one oxo-cyclononene 31 were also prepared. Cyclopentene 5b was subjected to a sequence of hydrogenation, NBS bromination, and treatment with powdered zinc to furnish the ring-expanded product 35. No such ring expansion occurred when the cyclohexaannulated compound 8 was treated with NBS followed by powdered zinc, leading to aldehyde 39. The spiro dihydrofuran derivative 19 was converted to the aldehyde 42 via the same reaction sequence used to fragment cyclopentene derivative 5b.

Even eight-membered rings (such as in 2) can be formed by ring-closing metathesis of glucose derivatives such as 1. Enantiomerically pure tricyclic spiro compounds can also be prepared.

Methods for the annulation of carbohydrates have found extensive applications in organic synthesis. We report here a new protocol for the stereoselective conversion of glucose into an enantiomerically pure cyclopentane aldehyde 22. The readily available epoxide 15 was reacted with allyl Grignard to produce alcohol 16 in 86% yield. Swern oxidation followed by epimerization using triethylamine in N,N-dimethylformamide furnished the ketone 17 also in 86% yield. Regioselective deprotonation with lithium hexamethyldisilazane in THF was followed by methylation with methyl iodide and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidone as cosolvent to give 80% yield of ketone 18. Oxidation of ketone 18 by the Wacker procedure gave the 1,4-diketone 19 in 56% yield. Intramolecular aldol condensation occurred readily on treatment of diketone 19 with potassium tert-butoxide in toluene to furnish a 90% yield of enone 20. Treatment with N-bromosuccinimide produced the bromoester 21 in 72% yield, which was reduced to a mixture of aldehydes 22 (61%) and 23 (14%) with zinc shot in 2-propanol.

Carbohydrate derivatives 1a, 1b, 3a and 3b have been subjected to copper(I) catalysed photoannulation to produce tetracyclic products 2a, 2b, 4a and 4b respectively as single enantiomers. The same reaction carried out on substrates 5a and 5b leads stereoselectively to the spiro products 6a and 6b respectively. Photoannulation of substrate 7 gave an approximate 1:1 mixture of spiro products 8 and 9. A mechanistic rationalisation of these results is proposed.Synthetic chemists have used carbohydrates as polyhydroxylated chiral starting materials for many years. 1 When the chosen target molecule in these ventures is cyclic, methods for the annulation of the carbohydrate starting material are required, and there are many varied strategies to achieve this objective. 2 One potentially useful method for carbohydrate annulation involves a [2+2] photoannulation. To the best of our knowledge there are three applications of intramolecular enone-olefin [2+2] photoannulation in a carbohydrate example, 3 in which stereoselectivity was not always observed. There are also two examples of intermolecular enone-olefin [2+2] photoannulation on sugar derivatives, one of which occurs in low yield with poor stereoselectivity. 4 We now report the stereoselective formation of several cyclobutane carbohydrate derivatives, in good yield, via the copper(I) catalysed [2+2] photoannulation of the corresponding unactivated 1,6-dienes.The formation of coordination complexes between copper(I) and olefins is well known. 5, 6 Applications of these complexes in catalysed photoannulation reactions has been studied by Salomon for many years. 7 In particular copper(I) catalysed [2+2] cycloaddition has been especially successful. Coordination of the copper(I) to both olefins produces a complex which absorbs the light and cyclizes. The product does not coordinate, and so is released from the copper, which then coordinates another molecule of diene to complete the cycle.Continuing our interest in new methods for carbohydrate annulation 8 we have investigated the application of the copper(I) triflate catalysed [2+2] photoannulation to this problem. We were particularly interested to see if the promising results of Salomon and Ghosh, 9 on the stereocontrol of these reactions, could be applied in carbohydrate examples to produce single enantiomerically pure diastereoisomers.Downloaded by: UC Santa Barbara. Copyrighted material.