Cyclohexadiene amino acids

This concept was extended to imines derived from a-amino acids. Several imines 8 react with cyclopentadiene (4) and 1,3-cyclohexadiene (9) yielding adducts 10 and 11 with good to excellent diastereoselectivity, while addition to acyclic dienes 12 proceeds with moderate selectivity68. 

The extremely large fraction of the total tritium in phenylalanine and tyrosine for /3-labeling of ribonuclease and chymotrypsinogen with TI can be understood in terms of a mechanism involving the addition of iodine atoms to aromatic rings, followed by reaction of the carbon radical with TI to give the cyclohexadiene derivative, which will tend to aromatize with loss of HI or TI to yield the tritiated parent amino acid as shown below. 

In the reaction of the a-amino acid derivative 73 with 1,5-cyclooctadiene catalyzed by ruthenium complex 2 depicted in Scheme 2.29, an enyne CM followed by an RCM was coupled in a domino manner with an initial ROM of the cyclic diene [17b,cj. The resulting enantiomericaUy pure 1,3-cyclohexadiene 74 was then used to construct the diketopiperazine core of the scabrosin epidithiodiketopiperazine antibiotics [17cj. 

The intramolecular Diels-Alder cyclization of cyclohexadiene-l,2-dicarboxylic anhydride-derived diester-tethered triene (86) produces the cycloadducts in a ratio of 7 1 (Scheme 31). The intramolecular Diels-Alder reactions of amino acid-derived trienes (87) yield cycloaddition products (88) and (89) which are mainly cw-fused and derived from the exo-transition states (Scheme 32). A key reaction in the synthesis of the natural product momilactone A is the transannular Diels-Alder cyclization of the trans-trans-cis alkene (90) to the trans-syn-trans tricycle (91) (Scheme 33). The Diels-Alder cycloaddition of 1 l-oxapentacyclo[6,5,2,2 0 0 ]-heptadeca-4,14,16-triene-4,5-dicarboxylic anhydride (92) with cyclopentadiene proceeds with 5yn-facial selectivity to produce syn,endo and syn,exo cycloadducts (93) and (94)... 

Waldman et al. [7] extended and improved the asymmetric methodology by utilizing (/ )- and (.S)-amino acid ester hydrochlorides as chiral auxiliaries in analogous aza Diels-Alder processes. A variety of chiral amino acids were evaluated, with isoleucine providing the best asymmetric induction. A typical protocol involves reacting (iS)-isoleucine methyl ester hydrochloride with aqueous formaldehyde in the presence of the diene in water-tetrahydrofuran (11/1) at 0°C. Use of cyclopentadiene provides the corresponding azanor-bomene products, 16 and 17, in excellent stereoisomeric ratio (93/7) in 57% yield (Scheme 2.1). In the case of the less-reactive cyclohexadiene, the corresponding diastereomers are formed at 25 C in a 80/20 ratio in 35% yield. 

Chemical Name 7-[ (Amino-1,4-cyclohexadien-1-yl-acetyl)amino] -3-methoxy-B-oxo-5-thia-1 -azabicyclo [4.2.0] -oct-2-ene-2-carboxylic acid... 

Chemical Name 6-[D-2-amino-2-(1,4-cyclohexadien-1-vl)acetamido] -3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0] heptane-2-carboxylic acid... 

CN [6 -[6a,73( )]]-7-[ amino-l,4-cyclohexadien l-ylacetyl)amino]-3-methyI-8-oxo-5-th a-l-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid... 

Rubin C 2-Amino-5-[(4-amino-3-sulphophenyl)(4-imino-3-sulpho-2,5-cyclohexadien-l-yhdene)acid disodium salt... 

Sudo and Saigo153 reported the application of ds-2-amino-3,3-dimethyl-l-indanol derived l,3-oxazolidin-2-one 231 as a chiral auxiliary in asymmetric Diels-Alder reactions. The TV-crotonyl and TV-acryloyl derivatives were reacted with cyclopentadiene, 1,3-cyclohexadiene, isoprene and 2,3-dimethyl-l,3-butadiene, using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded the expected cycloadducts in moderate to high yields (33-97%) with high endo selectivities and high de values (92% to >98%). 

Currently available chiral Diels-Alder catalysts have major limitations with regard to the range of dienes to which they can be applied successfully. Indeed, most of the reported catalytic enantioselective Diels-Alder reactions involve reactive dienes such as cyclopentadiene, but 1,3-butadiene and 1,3-cyclohexadiene have not been successfully utilized without reactive 2-bromoacrolein. To solve this problem, a new class of super-reactive chiral Lewis acid catalysts has been developed from chiral tertiary amino alcohols and BBr3 [24] (Eq. 8A.13). This type of chiral super Lewis acid works well for a,fj-acetylenic aldehydes [25],... 

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