Thermolysis of 2-(3-Butyn-1-oxy)-2-methoxy-5,5-dimethyl-.DELTA.3-1,3,4-oxadiazoline in Solution. A remarkable Cascade of Carbene and Other Reactions

Abstract

Thermolysis of 2-(3-butyn-l-oxy)-2-methoxy-5,5-dimethyl-A3-l,3,4-oxadiazoline in benzene or in toluene affords (la,laa,3aa,6aa,6ba)-methyl la-ethenyloctahydro-6a-methoxy-2,2-dimethyl-3,6dioxacyclobut[cd]indene-l-carboxylate in up to 74% yield. A reasonable mechanism involves about ten sequential steps and some novel intermediates including a dioxycarbene, a cyclopropenone ketal, and a vinylogous dioxycarbene. Various steps in the proposed mechanism were inferred from the results of deuterium-labeling experiments and from the incorporation of key intermediates from solution into the final product.Recently we reported the preparation of 2,2-dialkoxy-A3-l,3,4-oxadiazolines, such as 2, by oxidation of the

Intermolecular Reactions of a Foiled Carbene with Carbonyl Compounds: The Effects of Trishomocyclopropyl Stabilization

“…Δ 3 -1,3,4-Oxadiazolines are popular and versatile sources of free carbenes that can be liberated by either photolysis or thermolysis. − ,− The diastereomeric precursors r - 10 and s - 10 were used separately herein to generate carbene 1 (Figure ). They were dissolved in either PhC­(O)­H or PhC­(O)­Me and heated to T = 165 °C until fully decomposed (Scheme ).…”

“…are popular and versatile sources of free carbenes that can be liberated by either photolysis or thermolysis [71][72][73][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115]. The diastereomeric precursors r-10 and s-10 were used separately herein to generate carbene 1(Figure 4).…”

Heterocycles Derived from Heteroatom-Substituted Carbenes

“…67 The cyclization of (alkynyl-1-oxy)-alkoxycarbenes has been extensively studied by Warkentin's group. [68][69][70] The (alkynyl-1-oxy)methoxycarbenes 250, generated by thermolysis of the corresponding oxadiazoline precursors 249, cyclized by carbene attack of the C-C triple bond, leading to a new carbene. The endocyclic or exocyclic 3,3-dialkoxyvinylcarbenes 252 or 254 apparently form by way of the highly strained dialkoxycyclopropene 251.…”

“…71 Thermolysis of the oxadiazoline precursors 249c and 249d in the presence of benzylidenemalononitrile or DMAD led to exocyclic vinylcarbenes which underwent [3 + 2]-cycloaddition with benzylidenemalononitrile or DMAD to form bicyclic heterocycles 256-260 in good yields (Scheme 46). 69 If the oxadiazoline 249a 68 was heated in toluene for 30 h alone, a very strained tricyclic cyclobutanone ketal 264 was formed in 74% yield. A mechanism was postulated including addition of 3,3-dioxyvinylcarbene to acetone as a key step.…”

2-Alkoxy-2-amino-Δ3-1,3,4-oxadiazolines as Novel Sources of Alkoxyaminocarbenes

“…) CH 3 ), respectively. Dialkoxycarbenes are known to participate in intermolecular 21 and intramolecular 22 reactions with activated triple bonds. In order to probe the reactivity of our azaoxacarbenes, oxadiazoline 7f was thermolyzed in benzene with 1.1 equiv of methyl propiolate (Scheme 4).…”