L-Diethylamino-3-

Dipolar cycloaddition of pyrido[2,l-A][l,3]thiazinium betaine 507 (R = Me) with 1-diethylamino-l-propyne afforded cycloadduct 508, from which quinolizin-4-one 509 formed by a rapid cheletropic extrusion of COS (Scheme 53) <1995T6651>. 1,4-Dipolar cycloaddition of 507 and 4-phenyl-l,2,4-triazoline-3,5-dione yielded 511 (via 510) <1995H(41)1631> and 512 <1995T6651>. 

In the course of investigation of reactivity of the mesoionic compound 44 (Scheme 2) the question arose if this bicyclic system participates in Diels-Alder reactions as an electron-rich or an electron-poor component <1999T13703>. The energy level of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals were calculated by PM3 method. Comparison of these values with those of two different dienophiles (dimethyl acetylenedicarboxylate (DMAD) and 1,1-diethylamino-l-propyne) suggested that a faster cycloaddition can be expected with the electron-rich ynamine, that is, the Diels-Alder reaction of inverse electron demand is preferred. The experimental results seemed to support this assumption. 

A range of 2,2-bis(trifluoromethyl)-l,3-oxazepin-5-ones (334) has been prepared by the reaction of oxazolidin-5-ones with 1-diethylamino-l-propyne (75TL3223). l,3-Oxazepan-2-one has been prepared by the Beckmann rearrangement of tetrahydro-2-pyranone oxime. 

Dipolar cycloaddition of anhydro pyrido[2,l-b][l,3]thiazinium hydroxides (128) with aryl isocyanates and dimethyl acetylenedicarboxylate gave pyrido[l,2]pyrimidines (129) and quinolizine-l,2-dicarboxylates (130), respectively (76CB3668). 1,4-Dipolar cycloaddition of pyrido[2,l-h][l,3]thi-azinium betaine (131, R = Me) with 1-diethylamino-l-propyne afforded cycloadduct 132, from which quinolizin-4-one 133 formed by a rapid cheletropic extrusion of carbonyl sulfide (93TL5405 95T6651). 1,4-Dipolar cycloaddition of anhydro 4-hydroxyl-2-oxo-6,7,8,9-tetrahydro-2//-pyrido-[2,l-b][l,3]thiazinium hydroxides (131) and 4-phenyl-l,2,4-triazoline-3,5-dione yielded 135 via 134 [94H(39)219 95H(41)1631] and 136 (95T6651). 

Ethers of the 1,2-benzisothiazole 1,1-dioxides (35 R = Et, Me3Si) have been shown to form 1,2-benzothiazepines 12 (R = Et, Mc Si) when treated with 1-diethylamino-l-propyne 37 <1996T3339>. These ethers 12 may be hydrolyzed to the ketone 13 (see also Section 13.07.2.1), which in the solid state is in equilibrium with the enol 12 (R = H) on the basis of infrared (IR) evidence (Scheme 3). In solution (CDCI3), only the keto form 13 was detectable by H nuclear magnetic resonance (NMR). 

Diethylamino-methan- -diethylester XII/1, 412, 445, 485 E2, 349, 370 aus Phosphorigsaure-diethylester, Diethylamin und Formaldehyd XII/1, 484 Diethylamino-methan- -ethylester XII/1, 412 aus Diethylamino-methan-phosphansiiure-di-ethylcster und Kaliumhydroxid Xll/l, 410 1-Diethylamino-l-methyl-ethan- -diethylester XII/1, 485... 

A-Tosylsulfimines, e.g., 250, are converted into 1,2-benzothiazepines 252 by triethylamine (Scheme 142). In the absence of base the intermediate 251 can be isolated <1981J(P1)1037>. 1,2-Benzothiazepine 1,1-dioxides 254 are prepared by ring expansion of the 1,2-benzoisothiazole derivatives 253 upon treatment with 1-diethylamino-l-propyne (Scheme 143) <1996T3339, CHEC-III(13.07.4.2)241>. 

The hydration reaction is catalysed by amines but apparently it can occur at elevated temperatures without added catalyst. Thus, 1-dimethyIamino- and 1-diethylamino-l-buten-3-yne (129) (R = R = Me, R = R = Et) undergo hydration at room temperature in the presence of the corresponding amine, but fail to do so when they are shaken alone with water for 24 hours, and give only resins when the aqueous solutions are heated. On the other hand, the pyrrolidino (146) and piperidino (147) analogues undergo hydration when they are heated with water . ... 

Saccharin pseudochloride 112 (R = C1) reacts with 1-diethylamino-l-propyne to give 113. When the corresponding 3-ethoxy derivative 112 (R = OEt) was treated with the same alkyne, a ring-expansion product 114 (R = OEt) was isolated. On the other hand, the analogous thiazepine 114 (R = OSiMc3) is obtained, together with the ketone derived by hydrolysis of the silyl enol ether, by the reaction of saccharin with BuLi/trimethylsilyl chloride (TMCS)... 

Under kinetic control 1-(diethylamino)-l-propyne preferentially adds alcohols syn to hydrogen. If the reaction is carried out at room temperature in the presence of a Lewis acid, fast equilibration of ketene A2,0-acetals occurs and the rearrangement proceeds via the thermodynamically favored (Z)-isomer. Slow addition of allylic alcohols at 140 °C suppresses the rapid equilibration thus making the rearrangement of the kinetic ketene, Y,0-acetal intermediate competitive with cisitrans isomerization to the thermodynamically more stable intennediate, e.g.. formation of 14 and 15 (Table 9). 

Thus, pentacarbonylmethoxymethyl-(or phenyl-)carbenechromium, -molybdenum or -tungsten react at RT with diethylaminoethyne or 1-diethylamino-l-propyne to give, in good yields, amino-stabilized carbenes ... 

In another group of (2 + 2)-cycloaddition reactions, the heterocyclic nucleus reacts via an electron-deficient carbon-carbon or carbon-nitrogen double bond with electron-rich aminoacetylenes (ynamines). For instance, thiete 1,1-dioxides, JV-benzylmaleimide, and 2,3-bis(methoxycarbonyl)-7-oxabicyclo( 2.2.1 lhepta-2,5-diene reacted with 1-diethylamino-l-propyne and with 1 -phenyl-2-( 1 -pyrrolidinyl)-acetylene to give the (2 + 2)-cycloadducts 48, 49, and 50, respec-tively.35,37,53 The latter product was thermally rather unstable, and its structure was identified on the basis of its conversion with 2,4,6-tri-methylbenzonitrile oxide into 51.53 (2 + 2)-Cycloaddition via a carbon-nitrogen double bond has been reported to take place in the reactions of 3,3-dimethyl-3//-indoles and 3,4-dihydroisoquinoline with ynamines, e.g., l-dimethylamino-2-phenylacetylene, in the presence of boron trifluoride.54 The (2 + 2)-cycloadducts 52 and 53 were not isolated, but... 

Reactions of electron-r/cA acetylenes with heteroaromatic compounds are rare. Such (2 + 2>cycloadditions have been proposed as the first step in the boron-trifluoride-catalyzed reaction of isoquinoline with l-dimethylamino-2-phenylacetyleneM and in the reaction of 1,2,4-triazines with 1-diethylamino-l-propyne, 1 but no experimental... 

Across carbon-carbon multiple bonds The [2+2] cycloaddition reaction of ketenimines to acetylenic compounds affords 2-azetines and six-membered ring 2-iminotetrahydropyridine derivatives. For example, reaction of 1-diethylamino-l-propyne with iV-methyldiphenylketenimine in acetonitrile for seven days gives an equimolar mixture of the [2+2] cycloadduct 13 and the [2+2+2] cycloadduct 14... 

---