8-Phenylmenthyl acrylate cycloadditions

Cycloadditions. The asymmetric Diels-Alder reaction of phenylmenthyl acrylate with 5-benzyloxymethyl-cyclopentadiene in the presence of Aluminum Chloride produces an 89% yield of the endo cycloadduct (eq 1), accompanied by 7% of the exo adduct. This provides a useful intermediate for the preparation of various prostaglandins. The Tin(IV) Chloride and Titanium(IV) Chloride catalyzed reactions with Cyclopenta-diene deliver a mixture of endo and exo adducts in 89% de, and 90% de, respectively (eq 2). The TiCU reaction gives an 89 11 endo. exo ratio, while the SnCU reaction gives an 84 16 endoiexo ratio. From a practical point of view, the titanium and tin catalysts are the best of the various Lewis acids surveyed. The use of TiCl4 is also the most effective for the reaction of the acrylate... 

Dipolar Cycloadditions. The asymmetric induction for a 1,3-dipolar cycloaddition of phenylmenthyl acrylate is not as good as in the [4 + 2] cycloadditions. The thermal decomposition of di-azofluorene in the presence of the acrylate produces the spirocy-clopropane in 96% yield, but with only a 20% de (eq 4). ... 

Most importantly, even asymmetric induction with a maximum of 64 % d.e. is achievable by starting with optically active 8-phenylmenthyl acrylate" . Recently the Binger group has also reported the cycloadditions to alkynylsilanes forming 4-methylene-1-cyclopentenes (equations 194 and 195)" However, in many examples regiochemical problems concerning methylenecyclopropane as well as alkyne substituents might limit practical application. 

The formation of spirocyclopropanes from the reaction of diazodiphenylmethane and ( )-8-phenylmenthyl esters of acrylic acid and methyl fumarate occurred with a modest level of diastereofacial selectivity (136). In contrast, diastereoselectivities of 90 10 were achieved in the cycloadditions of diazo(trimethylsilyl)methane with acrylamides 65 derived from camphor sultam as the chiral auxiliary (137) (Scheme 8.16). Interestingly, the initial cycloadducts 66 afforded the nonconjugated A -pyrazolines 67 on protodesilylation the latter were converted into optically active azaproline derivatives 68. In a related manner, acrylamide 69 was converted into A -pyrazolines 70a,b (138). The major diastereoisomer 70a was used to synthesize indolizidine 71. The key step in this synthesis involves the hydrogenolytic cleavage of the pyrazoline ring. 

Simpler, open-chain, chiral alkenes have also been employed in [3 + 2]-cycloaddition reactions in order to obtain face selectivity of the addition. The introduction of chiral alcohols such as ( —)-(l/ ,27 ,5S)-menthol into acrylic esters provides a simple entry into this field however, the conformational variability of such molecules allows for only relatively low stereoselectivities.The same is true for the (— )-(l /J,2i ,4i )-bornyl and (— )-(l 7 ,27 ,55)-8-phenylmenthyl derivatives. ... 

---