2-alkyl-3-ethenyl

Exclusive trims attack of the nucleophile is also observed with 2,3-epoxycyclopentanones 1559. In contrast to 2-alkyl- and 2-methoxy-substituted cyclopentanones, preferential trans attack to 2,3-epoxycyclopenlanones occurs with alkyl, ethenyl, and ethynyl nucleophiles. Thus, there is no assistance by the epoxidic oxygen for cis attack. Due to the geometry of the molecule, chelation-controlled cis attack is not possible39 60. 

Whereas inter- and intramolecular Diels-Alder reactions normally require electron-deficient dienophiles, the 67r-electrocyclization proceeds with a large vaiiety of substituents on a hexatriene. In one such approach, the intramolecular Heck-type reaction of a 2-bromo-1 -en-(ft> — l)-yne 66 is used as a trigger to initiate an intermolecular Heck coupling with an alkene to form the conjugated 1,3,5-hexatriene 67 which eventually cyclizes in a 67T-electrocyclic process (Scheme 3-21) [173]. In many cases, aromatization of the cyclohexadiene 68 formed primarily occurs to yield carbo- and heterobicyclic compounds of type 70 [173a,b]. But with alkyl ethenyl ethers the cyclohexadienes 69 can be obtained in moderate yields [173b]. 

NITRILES, alkylation of, 55, 91 NITRILES, a-vinyl- [Nitriles a-ethenyl-],... 

Similar behaviour has been observed in the photoreaction of methyl a-cyano-4-[2-(2-pyridyl)ethenyl]cinnamate (7 OMe) crystals in which the yield of [2.2] paracyclophane reached 65% on irradiation at — 78°C (see Scheme 10 p. 153) (Hasegawa et al., 1989b). From the crystal structure analysis of the same type of [2.2] paracyclophane, which is topochemically derived from alkyl a-cyano-4-[2-(4-pyridyl)ethenyl]cinnamate crystals, a highly strained molecular shape is confirmed in which two phenylene rings are severely bent (Maekawa et al., 1991b). 

Versions of these aminocyclopropanations of terminal alkenes can also be applied intramolecularly. Terminally ethenyl-substituted N,N-dialkylcarboxamides such as 67 yield l-(dialkylamino)bicyclo[n.l.O]alkanes such as 68, while (w-alkenylamino)carboxa-mides such as 69 and 71 lead to 1 -alkyl-2-azabicyclo u.l.0]alkanes such as 70 and 72 (Scheme 11.20) [86,118], and N-allylamino acid N,N-dialkylamides furnish bicyclic diamines (see below). 

Brown and Suzuki have shown that treatment of trialkylboranes with ethenyl-(Scheme 42, Eq. 42a) and ethynyloxiranes (Scheme 42, Eq. 42b) in the presence of a catalytic amount of oxygen, affords the corresponding allylic or allenic alcohols. The mechanism may involve the addition of alkyl radicals to the unsaturated system leading to l-(oxiranyl)alkyl and l-(oxiranyl)alkenyl radicals followed by rapid fragmentation to give alkoxyl radicals that finally complete the chain process by reacting with the trialkylborane [104-106]. 

The question of configurational stability has been investigated first for vinylidene carbenoids and, more recently, for alkylcarbenoids. Vinyl anions are usually considered to be configurationally stable" ° the calculated inversion barrier of the ethenyl anion 10 (R = H) is about 35 kcal mol (equation 4)" . Concerning lithioalkenes, this configurational stability has been confirmed experimentally for a-hydrogen, a-alkyl and a-aryl substituted derivatives . The inversion of vinylidene lithium carbenoids was already... 

S)-Pinanediol boronic esters 2 with (dichloromethyl)lithium produce (aS)-a-chloro boronic esters 3. The first experiments provided diastereomerie ratios in the range 75 25 to 98 2. The best results (>94 6) were obtained with phenyl, ethenyl, or 1-phenylethyl attached to the boron atom39 40. The diastereomerie ratios were estimated from the rotations of esters of derived secondary alcohols. It was subsequently found that zinc chloride catalysis of the rearrangement of the intermediate borate complexes 2 improved the yields, usually to 85-95%, with diastereo-meric ratios often >99 1 when R1 = alkyl, as shown by NMR measurements15,43. 

Anstclle der Amine + Katalysator konnen anch die gesondert hergestellten Lithium-amide eingesetzt werden, so z.B. bei der Oberfiihrung von Ethenyl- und Allyl-phosphanen in (2-Amino-alkyl)-phos-phane in siedendem Toluol (maBige bis gute Ausbeuten)7. 

Sn2 ring opening by attack of a nucleophile on an ethenyl substituent (e.g. Scheme 60) has assumed importance in natural products synthesis (80JCS(P1)2084, cf. 81JA5969). The cyclopentene oxide (63) is a versatile synthon for alkylated, functionalized cyclopentanes (Scheme 61) (81JA2112). 

In contrast, compounds such as chlorobenzene and chloroethene, in which the halogen is attached directly to a multiply bonded carbon atom, do not exhibit SNl-type reactions. Evidently then, unsaturated carbon cations such as phenyl or ethenyl are appreciably less stable (more difficult to form) than tert-alkyl cations ... 

The reason for the lack of SN2 reactivity in ethenyl or ethynyl halides may be that the attacking nucleophile is unable to react by the concerted inversion mechanism that invariably is observed with alkyl halides ... 

Lithioethenyl phenyl tellurium was not alkylated by 1-propyl iodide or allyl bromide. Only diphenyl ditellurium and ethenyl phenyl tellurium were isolated from the reaction mixtures1. 

Alkyl but-3-en-l-yn-l-yl tellurium and lithium in liquid ammonia form lithium al-kanetellurolates. The tellurium-ethenyl bond is broken in this reaction1. 

Compounds are systematically named in the density tables as alky (alkenyl, alkynyl, etc.) derivatives of benzene in the style <side chains>benzene. Side chains consist of one or more alkyl (alkenyl, alkynyl, etc.) radicals attached to the benzene ring. Thus names such as butyl, pentyl, heptyl refer to saturated straight chain radicals. Unsaturated side chains are named as radicals from the corresponding alkene, alkadiene, alkyne, etc. Examples are ethenyl, (1-propenyl), (2-butenyl), (2,3-pentadienyl), and (4-pentynyl). The numbers indicate the postion of the double and triple bonds. 

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