Prop-

The merits of (enantioselective) Lewis-acid catalysis of Diels-Alder reactions in aqueous solution have been highlighted in Chapters 2 and 3. Both chapters focused on the Diels-Alder reaction of substituted 3-phenyl-1-(2-pyr idyl)-2-prop ene-1-one dienophiles. In this chapter the scope of Lewis-acid catalysis of Diels-Alder reactions in water is investigated. Some literature claims in this area are critically examined and requirements for ejfective Lewis-acid catalysis are formulated. Finally an attempt is made to extend the scope of Lewis-acid catalysis in water by making use of a strongly coordinating auxiliary. 

Diacetylene reacts with ethyleneglycol in the presence of alkalis at 75-140°C to form a mixture of 2-(prop-2-ynyl)-l,3-dioxolane (36), 2-(propa-l,2-dienyl)-l,3-dioxolane (37), and 2-(prop-l-ynyl)-l,3-dioxolane (38) (1-5 h, yield 66%), the ratio of which depends on the experimental conditions (74ZOR953). 

Di- and tetraynes with hydrogen sulfide in an alkaline medium at 20-80°C form systems containing linked thiophene cycles. Thus, l,4-dithienylbuta-l,3-diyne (47) forms 2,5-di(2-thienyl)thiophene (48) in 78% yield, whereas octa-2,4,6-tiiyn-l-ol (49) under the same conditions gives 5-hydroxymethyl-2-prop-1-ynylthiophene (50) in 50% yield (77HOU947). 

Finally, many [4+2] cycloaddition strategies utilizing various substituted thiophenes as dienes have been reported. The reaction between 2-(prop-l-enyl)-l-benzo[fo]thiophene and 3-chlorocyclobut-3-ene-l,2-dione followed by bromination and loss of HBr gives a... 

Within the synthesis of pyrethroids, which are used as insecticides, (5)-4-hydroxy-3-methyl-2-prop-2-ynyl-cyclopent-2-enone is needed. Starting from a racemic mixture of the esterified... 

Room temperature conditions affected only the conversion, the reaction rate being smaller (entry 6). Noticeably, cyclization of 2-prop-2-ynyl-malonic acid monomethyl ester le and 2-phenyl-pent-4-ynoic acid If, also occurred with very good results (entries 7, 8). The obtained results may be ascribed to the LDH support, which exhibits enough basic properties to activate the unsubtituted acetylenic carboxylic acids. Basically, the composition of the LDH exhibits only a very minor influence in these reactions. 

Begley MJ, Crombie L, Simmonds DJ et al (1974) X-ray analysis of synthetic (45)-2-(prop-2 -enyl)rethronyl (lJ )(3J )-chrysantemate 6-bromo-2,4-dinitrophenylhydrazone and (31 ) chiroptical correlation with the six natural pyrethrin esters. J Chem Soc Perkin Trans 1 879-913... 

Synonyms (PGDN) 1,2-Propylene glycol dinitrate propylene glycol dinitrate 1,2-prop anedio 1, dinitrate propylene dinitrate isopropylene nitrate methynitroglycol ATSDR 1995... 

Reactions of various l-(l,2-propadienyl)cyclopropanols having a substituent at the 1- or 3-position of the propadienyl moiety 55 proceed smoothly at between 0°C and room temperature with 1.1 mole amounts of Co2(CO)8 in either THF or ethyl acetate, and various 2-monosubstituted or 2,3-disubstituted 1,4-hydro-quinone derivatives 58 are obtained in good yields (Scheme 25). In particular, 1-(1,2-propadienyI)cycIopropanoI having the ferf-butyldimethylsilyl group at the 1-position of the 1,2-prop adienyl moiety gives a high yield of the silylated hydroquinone. 

Irradiation of 2-(prop-2-enyloxy)- and 2-(but-2-enyloxy)cyclohex-2-enones gives 2-oxabicy-clo[2.1.1]hexane and -[3.1.1]heptane derivatives, respectively,17 while 2-(but-3-enoyIoxy)- (7, n = 1) and 2-(pent-4-enoyloxy)cyclohex-2-enone (7, n = 2) afford the cyclohexanone-annulated 2-oxabicyclo[3.2.0]heptan-3-one (8, n = 1) and -[4.2.0]octan-3-one (8, n = 2) derivatives, respectively.18... 

Allylcyclopent-2-enones photoisomerize regioselectively to tricyclo[3.2.1.03 6]octan-2-ones 40 42 Similarly, 2-acetyl- or 2-methyl-2-(prop-2-enyl)-furan-3(2/y)-ones or -thiophen-2-ones afford the corresponding 7-heteratricyclooctan-2-ones 15.43,44 Photolysis of 5-(pent-4-enyl)-3-phenylcyclopent-2-enone yielded only 9-phenyltricydo[5.2.1.03-9]dccan-10-one (the straight cycloadduct).45... 

Irradiation of 2,5,5-trimethyl-2-prop-l-ynylcyclopentanone in pentane (0.1 M) for 72 hours gave, with 70% total conversion, the cyclobutane 3 as the major product (38%) together with various open-chain products and cyclopentene derivatives.150... 

Direct ring contraction of cyelohexenes to vinylcyclobutanes was observed on irradiation of 4-methyl-5,5-diphenylcyclohex-2-enone to give 3,3-diphenyl-2-prop-l-enylcyclobutanone (la) in 93-97% yield, while the 4,5,5-triphenyl derivative gave cyclobutanone substituted EjZ-isomeric styrenes 1 b in only 20% yield.56... 

Acetoxime, A zl do Derivative (Azido acetoxime, Triazo acetoxime or 1-Azi do-2-prop aneoxime), CH,. C( NOH). CH,. N mw] 14.11, N49-10%. Col oil, bp 84° at 2 mm with partial decompn. Was prepd from azidoacetone and hydroxyl-amine hydrochloride in aq soln contg some soda ash. When an attempt was made to distil 50g of azidoacetoxime at 2 mm, about 25 g distilled off at 84° while the residue in the flask gradually darkened and then violently exploded... 

Anilino-2,3-propanediol 3-Anilino-l,2-prop anediol y-Anil inopropyleneglycol ... 

A protropic shift may be induced to effect double bond migration in the side chain by heating the allyl phenyl ether with methanolic potassium hydroxide when 2-(prop-l-enyl) phenol is formed (Expt 6.108). 

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