Ring Experimental Procedures

A number of other, related compounds along with detailed experimental procedures are reported by Atkins, Richman and Oettle. Rings of other sizes and different leaving groups distinguish the latter work from that previously cited. In this case, as in the pre-... 

It is the purpose of this chapter to describe a number of ring enlargement and simultaneous ring enlargement-ring contraction procedures which should be of general use. Recommended illustrative experimental procedures are given. 

Ring-contraction methods described in this chapter have been selected from the many examples reported in the literature on the basis of outstanding reliability and utility. When several adequate methods are available for accomplishing the same transformation only one, and hopefully the best, experimental procedure is presented. The author admits a predilection for methods which in his own experience have proved useful. 

The benzilic acid rearrangement of steroid a-diketones is often the preferred method for ring contraction. Yields are generally excellent, and in several instances the reaction has been shown to be stereospecific. Preparation of the starting a-diketones is discussed below and illustrated with several excellent experimental procedures. 

The Diels-Alder reaction is the most important method for the construction of six-membered rings. For example it can be used as a step in a benzo-anellation procedure. The experimental procedure is simple, and yields are generally good side reactions play only a minor role. 

The only heterocyclic seven-membered ring system with maximum unsaturation containing six heteroatoms is 1,3A4,5,2,4,6-trithiatriazepine (1). The methoxycarbonyl derivative 2 is a minor product (14%) of the complex reaction of tetrasulfur tetranitride with dimethyl acetylenedicarboxylatc in refluxing toluene, which gives mainly dimethyl l,2,5-thiadiazole-3,4-dicarboxylate (3, 67%) (see Houben-Wcyl, Vol. E8d, pl54ff which includes an experimental procedure). Two other products are the trithiadiazepine 4 (5%, see Section 4.4.1.1.1.) and the 1,2,4-thiadiazole derivative 5 (3%).385... 

The technical production of poly(benzimidazole) (PBI) is also carried out in two steps. In the first step an aromatic tetramine is condensed with the diphenyl ester of an aromatic dicarboxylic acid at 220-260 °C, yielding a poly(amino amid) with elimination of phenol. Ring closure with elimination of water occurs in the second step (solid-phase polycyclocondensation), conducted at 400 °C and yielding the polybenzimidazole (experimental procedure, see Table 2.3). 

Scheme 9.17). The macrocycle (A) of Scheme 9.1 is the dpp-incorporating 30-membered ring 8 used earlier for making catenanes (see Protocol 5) it is sufficiently small to prevent release of the bis-porphyrin dumbbell. The preparation of 22+ takes place in seven steps.1819 One of the starting materials is 4-lithiotoluene 13, which may be obtained by direct interaction of an excess of freshly cut lithium with 4-bromotoluene 12 in ether under argon at reflux (Scheme 9.10).12 The resulting organolithium compound is titrated by the double titration method described by Gilman et alP The experimental procedure is very similar to that described in Protocol 1.

Experimental Procedure -- The surface tensions of Triton X-100 solutions, with or without other additives, were measured using a du Nouy ring tensiometer (Fisher Scientific Company) at 25°C. 

Nucleophilic substitution on the cyclopropane ring takes place during irradiation of a mixture of 7-bromobicyclo[4.1.0]heptane and diphenylarside in liquid ammonia giving (bicyclo[4.1.0] hept-7-yl)diphenylarsane (1) in 90% yield. The reaction involves radical-anion and radical intermediates. The experimental procedure used is identical to that for the corresponding phosphorus analog (section 5.2.1.1.15.). ... 

The ring closure of IV-acylimidates with nitriles and ammonia affords a practical route to trisubstituted 1,3,5-triazines which are otherwise not readily accessible.325 In the first step the nitrile reacts with ammonia to give the corresponding amidine 1, which subsequently reacts with an AT-acylimidate 2 to form the trisubstituted 1,3,5-triazine 3 (see Section 2.3.1.1.2.4. for further details and an experimental procedure). 

A pyrrolidine with two annulated dioxane rings 1 was prepared from D-mannitol1 and used as the lithium salt in enantioselective deprotonation and elimination reactions (Section C.). A recent improvement of the experimental procedure allows the preparation of a single diastereomer2. 

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