alternatively, R2 and R3, together with the carbon atom to which they are attached, combine to form a C3 7 cycloalkyl, a C3 7 cycloalkenyl, or a 5–6 membered heterocyclic ring consisting of carbon atoms, 1 ring heteroatom selected from O, N, NR10, and {HEAD ~ Sp}, and {TAIL ~ 0–2 double bonds} 
alternatively , R2 and R3 , together with the carbon atom to which they are attached , combine to form a C3 7 cycloalkyl , a C3 7 cycloalkenyl , or a 5–6 membered heterocyclic ring consisting of carbon atoms , 1 ring heteroatom selected from O , N , NR10 , and { HEAD ~ Sp } , and { TAIL ~ 0–2 double bonds }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL