Enantioselective synthesis of optically active α‐amino acids from glycine via Schiff base employing (+)‐N,N‐diisopropyl‐10‐camphorsulfonamide as a chiral template is described.

Synthesis and photochemistry of several title compounds 1-3 containing multiple chromophoric systems are described. The Diels-Alder reactions of 2,6,6-trimethylcyclohexa-2,4-dienone (5) with acetylenes 6a-d provided the adducts 7a-d, which upon hydrolysis furnished the desired bicyclo[2.2.2]octenediones 1a-d. Oximes 2a-d were prepared from diones 1a-d by treatment with hydroxylamine hydrochloride in pyridine. 5-Methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d were obtained via chemoselective Wittig reaction of the corresponding diones 1a-d. Bicyclo[2.2.2]octenediones 1a-c underwent chemoselective oxa-di-pi-methane rearrangement under sensitized conditions and suffered formal ketene extrusion upon direct irradiation. Direct irradiation of 1d afforded 11d via formal ketene extrusion but under sensitization it remained unchanged. Oximes 2a-d suffered ketene extrusion upon direct irradiation and E/Z isomerization under sensitized conditions. On the other hand, 5-methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d generally underwent 1,3-acyl shift. The plausible courses of all these photochemical processes are discussed.

4-Acetoxy-and 4-triflyloxy-2,6,6-trimethyl-2,4-cyclohexadienones were employed as non-dimerizing alternatives to 2,6,6-trimethyl-2,4-cyclohexadienone in Diels-Alder reactions with substituted acetylenes which facilitated the synthesis of substituted bicyclo[2.2.2]octen-2,5-diones, bicyclo[2.2.2]octadienones and 5-methylenebicyclo[2.2.2]octen-2-ones. During our studies on competitive photochemical rearrangements of bicyclo[2.2.2]octenone derivatives, a need for the synthesis of substituted bicyclo[2.2.2]octen-2,6-diones 1, bicyclo[2.2.2]octadienones 2 and 5-methylenebicyclo[2.2.2]oct-7-en-2-ones 3 (Figure 1) has arisen. While there are no efficient general methods available for the preparation of bicyclo[2.2.2]oct-7-en-2,5-diones 1 which are immediate precursors of 5-methylenebicyclo[2.2.2]oct-7-en-2-ones, there exist reports on synthesis of bicyclo[2.2.2]octadienones via Diels-Alder reactions of 2,4-cyclohexadienones and acetylene derivatives. 2 In principle, it should be possible to prepare bicyclo[2.2.2]octadienones of the required type 2 via DielsAlder reactions of appropriate acetylene derivatives with 2,6,6-trimethyl-2,4-cyclohexadienone (4). However, the tedious procedures involved in the preparation of 4 and its high propensity to dimerize have deterred us from using this approach. 3 It is pertinent to mention that despite the difficulties involved in the preparation and handling of 4, it has been used in the total synthesis of natural products on a number of occassions. 4During the search for an alternative to 4, 4-acetoxy-2,6,6-trimethyl-2,4-cyclohexadienone (5) prepared by Soukup et al., 5 attracted our attention. Interestingly, although 5 is quite stable and accessible in large quantities its DielsAlder chemistry has not been studied. 6,7 We herein report the first use of 4-acetoxy-2,6,6-trimethyl-2,4-cyclohexadienone (5) and 4-triflyloxy-2,6,6-trimethyl-2,4-cyclohexadienone (6) as attractive alternatives to 4 in Diels-Alder reactions with substituted acetylenes and a novel approach to title compounds 1-3 starting from readily available 4-ketoisophorone (7) (Schemes 1-3). Scheme 1Compound 5 was prepared from 7 following the procedure developed by Soukup et al. 5 The Diels-Alder reactions of 5 with substituted acetylenes such as ethyl propiolate (8a), dimethyl acetylenedicarboxylate (8b), phenylacetylene (8c) and diphenylacetylene (8d) were performed by heating 5 with two equivalents of an acetylene derivative at an appropriate temperature to obtain the adducts 9a-d in excellent yields (Scheme 1). 8 The regioselectivity observed in the reactions of 5 with 7a and 7c is noteworthy. Subsequent hydrolysis of 9a-d with potassium carbonate in ethanol or methanol at 0 o C proceeded smoothly to furnish the desired bicyclo[2.2.2]octendiones 1a-d in >93% yields. 9 It should be mentioned that compounds of type 1 were prepared by others from hydroquinone and maleic anhydride in very low yields (16%). 1 Figure 1Downloaded by: University at Buffalo (SUNY). Copyrighted material.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.